Best 9 Birch De Noel Recipes

BIRCH DE NOEL

Steps:

• Preheat oven to 350°F. Test each of the three eyes at stem end of coconut to find softest one. Use an ice pick and a hammer to pierce it, then drain the juice into a glass through a fine sieve and reserve for another use. Tap coconut with hammer until a palm-size piece of shell breaks off. Continue tapping around broken edge until shell begins to break apart. Place broken shell on a baking sheet; bake about 10 min- utes to loosen flesh. Remove from oven and let cool slightly. Pry out flesh with a paring knife. With a potato peeler, remove any remaining brown skin from flesh.
• Reduce oven temperature to 250°. Using a vegetable peeler, shave largest pieces of coconut into long curls, place on baking sheet, and bake until just dry but no color has developed, 15 to 20 minutes. Meanwhile, grate smaller coconut pieces on the small holes of a box grater. (You will need about 1/2 cup grated coconut for the filling.)
• Increase oven temperature to 400°. Coat a 12 1/2-by-17 1/2-inch rimmed baking sheet with cooking spray. Line with parchment paper; coat with cooking spray. Dust with cocoa; tap out excess. Whisk together cocoa powder, flour, and salt in a bowl. In a heat-proof mixer bowl set over (not in) a pan of simmering water, whisk together eggs, yolks, and granulated sugar until sugar has dissolved and mixture is warm to the touch. Attach bowl to mixer fitted with the whisk attachment and beat on medium-high speed 2 minutes. Raise speed to high; beat until mixture is pale and thick, about 4 minutes more.
• Sift cocoa mixture over egg mixture; carefully fold in with a large rubber spatula. When almost incorporated, pour melted butter down side of bowl; gently fold to combine. Pour batter into prepared sheet, and smooth top with an offset spatula.
• Bake until cake springs back when touched, 9 to 10 minutes. Place a clean kitchen towel on a work surface; dust generously with cocoa. Remove pan from oven and immediately turn cake out onto a wire rack lined with parchment. Invert onto prepared towel; remove parchment.
• While cake is still warm, gently roll, starting from one short side, into a log, incorporating towel. Let rolled cake cool completely. (This will give it a "shape memory," so it will be easier to roll again with filling.)
• Unroll cooled cake and transfer to parchment. Using a pastry brush, coat cake with rum. Using offset spatula, spread mousse over cake. Sprinkle with 1/2 cup reserved grated coconut.
• With a short end of cake facing you, roll carefully into a roulade. Wrap in a kitchen towel; secure with clothespins or large metal binder clips to hold roll in a tight round shape. Place on a baking sheet and refrigerate until firm, at least 2 hours and up to 1 day.
• Remove from refrigerator and unwrap. Use a serrated knife to trim ends of roll, cutting on the bias (starting 1 inch in from end on shorter side, and finishing 2 inches in, to create a wedge). Choose the more presentable trimmed end and place, cut-side up, on log, forming a branch. If desired, use other trimmed end for a second branch.
• Transfer log to a serving platter. Slide strips of parchment under perimeter of log (to keep platter clean). Use offset spatula to coat log with frosting, then attach one or both trimmed ends; coat with frosting. Remove parchment pieces. Decorate with meringue mushrooms, coconut shavings, and rosemary sprigs.

BUCHE DE NOEL

Steps:

• For the walnut biscuit:
• Preheat oven to 350 degrees F. Butter a half sheet pan, line with parchment paper, butter the paper and dust with flour. Whip the egg whites to soft peaks. Beat in both sugars and whip to a stiff, glossy meringue. Alternately fold the cake flour and egg yolks into the meringue in 3 batches, starting and ending with the flour. Fold in the nuts. Spread the batter evenly in the pan, and bake until the cake is pale gold, the center springs back when you press it lightly with your finger, and the edges start to pull from the sides of the pan, 10 to 12 minutes. ;
• For the pastry cream:
• Whisk the yolks, cornstarch, and the 40 grams sugar in a medium bowl; the mixture will be very thick, but try to whisk enough to remove most of the lumps. Put the 75 grams sugar in a medium saucepan and cook over medium heat until dark brown; don't worry if it crystallizes a bit. Turn the heat to low and whisk in the maple syrup, then whisk in the whisky, turn up the heat, and let simmer for 1 to 2 minutes to boil off the alcohol. Whisk the milk and vanilla bean scrapings into the caramel mixture and bring to simmer. Slowly whisk about half of the hot mixture into the yolks, then whisk that mixture back into the pot, bring to a boil, whisking, and cook, still whisking, until thickened. Remove from the heat and whisk in the butter, salt and maple extract. Pour into a shallow dish, press plastic wrap onto the surface, and chill until set and very cold, about 4 hours. Beat the cold pastry cream in a standing mixer until smooth. When ready to use, whip the cream until it is very stiff, then beat into the pastry cream. Chill until ready to use. ;
• For the buttercream:
• Put the sugar in a medium pot and add enough water just to moisten; use your fingers to wet the sugar evenly. Bring to a boil. While the sugar is heating, start beating the yolks and egg in a standing mixer with the whisk attachment. When the syrup reaches about 240 degrees F on a candy thermometer (softball stage), pour it into the yolks with the mixer still running, taking care not to pour it onto the whisk. Beat until cooled to room temperature. Beat in the whisky and the maple extract. Cream the butter in another mixing bowl using the paddle attachment. Beat in the cooled egg mixture until smooth. You can use it right away, or chill it overnight; if you chill it, rebeat when you are ready to assemble the cake. ;
• For the sugared cranberries:
• Have a cookie sheet or shallow dish and a slotted spoon next to the stove. Put the sugar in a medium pot and add enough water just to moisten; use your fingers to wet the sugar evenly. Add the cinnamon stick. Bring to a boil, add the cranberries, and immediately pull from the heat. Transfer the cranberries to the cookie sheet with the slotted spoon. Cool. ;
• For the maple tuiles:
• Cream the butter, maple syrup, vanilla bean scrapings and salt until smooth. Scrape the sides of the bowl and beat in egg whites until smooth. Beat in the flour. Let the batter rest and hour or so at room temperature, or overnight in the refrigerator. Bring to room temperature before baking. Preheat the oven to 325 degrees F. Line a sheet pan with a silpat. Using a stencil, smear the batter thinly on the silpat and bake until dark golden brown, about 6 to 8 minutes. Remove from the pan while still warm. If you want to shape the cookies, put them over a bottle or rolling pin while warm; let cool. If desired, brush lightly with luster dust. ;
• Assembly:
• Turn the cooled cake onto a piece of parchment or waxed paper with a long side near you. Spread the chilled pastry cream evenly over the surface, leaving a 2-inch border across from you. Using the parchment paper to lift, roll the cake as tightly as possible. Set seam side down on a platter or large pan, and chill for an hour or so. Frost the cake with the buttercream, smoothing the surface so it looks like bark. Decorate with candied cranberries, walnuts, orange peel, and tuiles. ;

BUCHE DE NOEL

Steps:

• PREPARE THE BISCUIT: Preheat oven to 420 degrees F. Place the whole eggs and yolks in a medium-sized mixing bowl. Add 1/3 cup of the granulated sugar and the milk. Whip with an electric mixer on medium-high speed, until the mixture lightens in color and triples in volume, about 6 minutes. Place the egg whites in a large mixing bowl, and whip at medium speed until foamy. Make French meringue by adding the remaining 2 tablespoons granulated sugar, 1 tablespoon at a time. When all the sugar has been added, increase mixer speed to medium-high and whip to stiff but not dry peaks, about 5 minutes.
• Use a rubber spatula to fold the egg mixture in batches into the meringue, incorporating it gradually so as not to deflate the meringue. When all the yolk mixture has been incorporated, place the flour in a fine-mesh sieve and sift over the mixture. Gently fold this in with the rubber spatula. Spread the batter evenly on a parchment-covered baking sheet, liberally dust the top of the biscuit with powdered sugar and place in the oven. Bake just until biscuit begins to brown on top, about 5 minutes. This will lock in the moisture, allowing you to roll the cake later without cracking it. Immediately after removing from the oven, run a knife around the inside of the baking sheet to loosen the cake from the sides. Remove cake from baking sheet and allow it to cool.
• PREPARE CHOCOLATE PASTRY CREAM: Make pastry cream as directed and let cool. Melt the chocolate in a double boiler or a mixing bowl placed over a bowl of simmering water, stirring it occasionally as it melts. When all of the chocolate is melted and smooth, remove it from heat, and add the cold pastry cream to the warm chocolate. Mix them together with a rubber spatula.
• PREPARE THE ROULADE: Place the biscuit on your work surface and soak with the flavored syrup. Spread the chocolate pastry cream evenly over the cake, spreading it all the way to the edges. Start at one long end and, rolling toward you, roll it into a tight cylinder. Place the roulade on a parchment covered baking sheet and place in the refrigerator for a few hours to set.
• PREPARE THE MUSHROOMS: Preheat oven to 250 degrees. Whip the egg whites on medium speed until foamy. Add the granulated sugar 1 tablespoon at a time, until you have volume, then add the rest of the sugar. Increase mixer speed to medium-high and whip until you have stiff but not dry peaks. Gently fold in the powdered sugar. Place the meringue in a large pastry bag fitted with a 1/4-inch plain tip. Pipe the mushroom pieces onto a parchment covered baking sheet. Make the stems by squeezing out a dime-sized mound of meringue, then pull the pastry bag straight up, leaving a small tail. Make the caps by piping 1/2-inch mounds onto the sheet. Sprinkle the caps with a little cocoa powder and place in the oven. Bake until firm and dry, about 1 hour, leaving the oven door cracked so moisture can escape. Remove from the oven and cool on a rack.
• PREPARE CHOCOLATE TREES: Make a cornet from parchment paper and fill half full with tempered chocolate. Pipe a long thick chocolate raindrop on a sheet of parchment paper. Draw a cake comb through the chocolate, starting at the center of the raindrop and moving from left to right. Repeat, starting at the center and moving from right to left. You should have a chocolate pine tree. Repeat for as many trees as you want. Allow the chocolate to set before peeling the parchment paper from it.
• PREPARE THE CHOCOLATE FENCE: Fill a cornet half full with the tempered chocolate, and pipe a 3 to 4-inch long railroad track, with the outside rails spaced about 2 inches apart and the inside rails spaced about 1/2-inch apart onto a sheet of parchment paper. Allow the chocolate to set before peeling the parchment paper from it.
• PREPARE THE COFFEE BUTTERCREAM: Place the egg yolks and whole egg in a large mixing bowl, and whip until thick, light, and tripled in volume, 5 to 7 minutes. Pour the water and granulated sugar into a 1-quart heavy-bottomed saucepan and place over medium heat. Insert a candy thermometer into the mixture. The sugar is ready when it reaches 250 degrees, or the soft ball stage. Pour the cooked sugar down the side of the bowl into the whipping eggs. Continue whipping the mixture until the outside of the bowl is warm but not hot, about 2 or 3 minutes. Add the butter all at once, and beat on medium speed until incorporated. Now whip on medium-high speed until thick, smooth and shiny, about 10 minutes. Remove about 1/3 cup and set aside. Add the coffee extract to the remaining buttercream and whip until well combined.
• ASSEMBLE THE BUCHE: Place the rolled cake on the platter you will use to serve it. Use a sharp knife to slice a 11/2-inch-thick slice from each end of the roll. These will become gnarls on the log. Spread a thick layer of buttercream over the buche. Place the ends or gnarls on top of the log, 1 at each end and cover with buttercream. Run a cake comb through the buttercream along the length of the buche, to make it look like bark. Place the buche in the refrigerator for about 15 minutes to let the buttercream set.
• MAKE THE IVY AND FLOWERS: Divide the unflavored buttercream evenly among 3 bowls and color each with 1 of the food colorings. Make 3 cornets from triangles of parchment paper, and fill one with pink buttercream, one with green, and one with yellow. Remove the buche from the refrigerator. Use the green icing cornet to make the ivy, by piping long curved lines along the length of the buche.
• Place small yellow dots along this stem, for the flower centers. Surround these with pink dots for the flower petals. Cut the tip of the cornet diagonally to make a point and fill it with green icing. Squeeze a dab of green buttercream out of the corner of each leaf.
• FINISHING THE BUCHE: Stick together the caps and ends of the mushrooms, using a dab of buttercream. Place the mushrooms, chocolate trees and chocolate fence on the buche. Dust the buche with powdered sugar and sprinkle with chocolate shavings. Refrigerate for 1 hour,then serve and enjoy!
• Sift together the cornstarch and half the sugar in a medium bowl, add the egg yolks and whisk until well combined. Pour the milk and remaining sugar into a 2-quart nonreactive heavy-bottomed saucepan and place over medium-high heat. While milk is heating, slice the vanilla bean in half lengthwise. Separate the seeds, and add both seeds and skin to the milk. Bring it to a boil. Carefully pour about half of the milk into the egg mixture, whisking so eggs don't scramble. Pour this mixture back into the saucepan and continue to whisk, as pastry cream thickens. Bring to a boil and continue to whisk and cook for 2 minutes more. Remove from heat, strain through a fine-mesh sieve, and add butter in small chunks if desired. Stir butter into cream until well incorporated. Pour pastry cream into an airtight container and put plastic wrap on top to prevent a skin from forming. Store in refrigerator for up to 3 days, until ready to use.
• SIMPLE SYRUP: Water, scant 1 1/4 cups Granulated sugar, 2/3 cup Liqueur, 2 1/2 tablespoons
• Place the water and sugar in a heavy saucepan over medium-high heat and bring to a boil, stirring occasionally. The sugar should completely dissolve. Remove from heat and pour into a mixing bowl. Cool before adding the liqueur.
• TEMPERED CHOCOLATE: When you melt chocolate, the molecules of fat separate. To put them back together, you temper it. One way to temper is to place the chocolate in the microwave, and microwave it on high power for 30 seconds at a time until the chocolate is melted. As it recrystallizes, it becomes tempered.

BUCHE DE NOEL

Steps:

• Preheat oven to 375 degrees F (190 degrees C). Line a 10x15 inch jellyroll pan with parchment paper. In a large bowl, whip cream, 1/2 cup confectioners' sugar, 1/2 cup cocoa, and 1 teaspoon vanilla until thick and stiff. Refrigerate.
• In a large bowl, use an electric mixer to beat egg yolks with 1/2 cup sugar until thick and pale. Blend in 1/3 cup cocoa, 1 1/2 teaspoons vanilla, and salt. In large glass bowl, using clean beaters, whip egg whites to soft peaks. Gradually add 1/4 cup sugar, and beat until whites form stiff peaks. Immediately fold the yolk mixture into the whites. Spread the batter evenly into the prepared pan.
• Bake for 12 to 15 minutes in the preheated oven, or until the cake springs back when lightly touched. Dust a clean dishtowel with confectioners' sugar. Run a knife around the edge of the pan, and turn the warm cake out onto the towel. Remove and discard parchment paper. Starting at the short edge of the cake, roll the cake up with the towel. Cool for 30 minutes.
• Unroll the cake, and spread the filling to within 1 inch of the edge. Roll the cake up with the filling inside. Place seam side down onto a serving plate, and refrigerate until serving. Dust with confectioners' sugar before serving.

MERINGUE MUSHROOMS FOR BIRCH DE NOEL

Steps:

• Heat oven to 200 degrees. Place Swiss meringue in an 18-inch pastry bag fitted with a large 3/4-inch round tip. Line two baking sheets with parchment paper. Pipe meringue, forming domes 1 to 2 inches in diameter. Pipe a stem shape for each dome. Bake for 1 hour; reduce heat to 175 degrees, and continue baking until meringues are completely dry to the touch but not browned, 45 to 60 minutes more.
• Fill a medium saucepan one-quarter full with water. Set over medium heat, and bring to a simmer. Place bittersweet chocolate in a heat-proof bowl, and set over simmering water. Turn off heat; stir chocolate occasionally until completely melted. Using an offset spatula, spread bottoms of domed meringues with chocolate; let sit at room temperature.
• Place white chocolate in a heat-proof bowl, and set over simmering water. Turn off heat; stir chocolate occasionally until completely melted. Allow to cool slightly. To create mushroom gills, spread white chocolate over dark chocolate; use a toothpick to create lines from the center of the cap's underside to the edges. Let set in a cool, dry place.
• Poke a small hole in the center of each mushroom cap using a paring knife. Dip the pointed end of each of the mushroom stems in melted white chocolate, and insert into hole in center of cap. Allow to set. Meringue mushrooms should be kept in an airtight container in a cool, dry place.

BIRCH DE NOEL - YULE LOG

Steps:

• Chocolate Cake:.
• Heat oven to 350°F
• Wrap coconut in a kitchen towel, and place in the oven for 15 minutes or longer.
• Remove from oven, and place on a work surface.
• Reduce oven temperature to 300°F
• Tap coconut with a hammer until it cracks in several places; break it in pieces (The white flesh should be slightly pulling away from hard shell).
• Carefully peel, keeping pieces of coconut as large as possible.
• Using a vegetable peeler peel largest pieces of coconut into long curls, and place on a baking sheet for 15 to 20 minutes, until just dry.
• Grate the smaller pieces on the box grater.
• You will need about 1/2 cup grated coconut for the cake filling.
• Heat oven to 400°F
• Line a 12x17 inch jellyroll pan with parchment paper and set aside.
• In a bowl of an electric mixer fitted with the whisk attachment, beat egg yolks on high speed until pale yellow, 4-5 minutes.
• Transfer to bowl, and set aside.
• Wash and dry mixer bowl.
• Place egg whites in bowl of electric mixer fitted with the whisk attachment on medium speed until soft peaks form, 1-2 minutes.
• Increase speed to high, and add sugar gradually, whipping until stiff peaks form.
• Transfer mixture to a large bowl.
• Using a rubber spatula, fold egg-yolk mixture into egg-white mixture; add cocoa powder and flour over top, and gently fold together.
• Pour batter into prepared pans; smooth top with an offset spatula.
• Bake until cake springs back when touched, 9-10 minutes.
• Remove from oven, and immediately turn cake out onto a wire rack lined with parchment paper.
• Peel parchment paper from top of cake, and cool completely.
• Place a clean kitchen towel on work surface.
• Transfer cake on parchment paper to towel.
• Using a pastry brush, coat cake with rum.
• Using an offset spatula spread the white-chocolate mousse over cake.
• Sprinkle with 1/2 cup freshly grated coconut.
• With a short end of cake facing you, roll carefully into a "log" shape on a kitchen towel, and secure with clothespins or large metal binder to hold the roll in a tight round shape.
• Place on a baking sheet, and refrigerate until firm, at least 2 hours.
• Remove from refrigerator, and unwrap.
• Using a serrated knife, trim the ends of the roll, cutting on the bias.
• Choose the more presentable end, and turn it side up, on the log, forming a branch or knot.
• If desired, use the other cut off end as a branch.
• Transfer the log to a serving platter.
• Slide 5-inch strips of parchment paper under the log to protect the tray while decorating.
• Coat with Seven Minute Frosting using an offset spatula.
• Remove parchment pieces.
• Decorate with Meringue Mushrooms, Snowy Chocolate Truffles, coconut shavings, and sugared Rosemary Sprigs.
• White Chocolate Mousse: Dissolve gelatin in 1/4 cup cold water, and set aside for 5 minutes.
• Place chocolate in the bowl of a food processor, and pulse until very finely chopped.
• Prepare an ice water bath; set aside.
• Place 3/4 cup cream in a small saucepan and bring just to a boil over medium-high heat.
• Add gelatin, and stir to dissolve completely.
• Pour into food processor with the motor running and process until chocolate mixture is smooth.
• Transfer to medium bowl and place over ice water bath.
• Chill until thick enough to fall from spoon in ribbons.
• Whip remaining 1 3/4 cups heavy cream to soft peaks.
• Fold into chocolate mixture (If not using immediately, refrigerate in an airtight container).
• Snowy Chocolate Truffles: Heat oven to 350°F
• Place almonds, if using, on a baking sheet, and bake until fragrant, about 10 minutes.
• Set aside to cool.
• Use a serrated knife to spread the chocolate.
• Place in a heat-proof bowl; set aside.
• In a saucepan, bring cream to a boil.
• Pour directly over chopped chocolate stirring to fully incorporate.
• Let sit for 10 minutes.
• Stir until completely melted and mixed.
• Allow to cool for 20 minutes.
• Stir in almonds, if using, and place in the refrigerator until set.
• Use a melon baller or 1 1/4 inch ice cream scoop to portion out chocolate.
• Roll the scoops of chocolate between palms to form 1-inch truffles.
• Refrigerate until ready to serve; dust with confectioners sugar before serving.
• Seven Minute Frosting: In a small heavy saucepan, combine 3/4 cup sugar, the corn syrup, and 2 tablespoons water.
• Heat over medium heat, stirring occasionally, until the sugar has dissolved.
• Rub a bit between your fingers to make sure there is no graininess.
• Raise heat to bring to a boil.
• Do not stir anymore.
• Boil, washing down sides of pan with a pastry brush dipped in cold water from time to time to prevent the sugar from crystallizing, until a candy thermometer registers 230F, about 5 minutes. (Depending on the humidity, this can take anywhere from 4-10 minutes).
• Meanwhile, in the bowl of an electric mixer fitted with the whisk attachment, whisk egg whites on medium speed until soft peaks form, about 2 1/2 minutes.
• Gradually add the remaining 2 tablespoons sugar.
• Remove the syrup from the heat when the temperature reaches 230F (it will keep rising as pan is removed from heat).
• Pour the syrup in a steady stream down the side of the bowl (to avoid splattering) containing the egg white mixture, with the mixer on medium-low speed.
• Beat the frosting on medium speed until it is cool, 5-10 minutes.
• The frosting should be thick and shiny. Use immediately.
• Sugared Rosemary Sprigs: Brush washed sprigs with a glaze of white sugar from a large egg thinned with a tablespoon of water, then coat in sugar, and let air dry.

BUCHE DE NOEL

Steps:

• Make chocolate genoise and mousse, ganache icing, and meringue mushrooms.
• To assemble cake, carefully unroll genoise on the back side of a baking sheet (discard the plastic wrap and waxed paper, but keep the towel). Spread chocolate mousse evenly on cake to within 1 to 2 inches of one long end. Reroll cake, starting from other long end, using towel to help roll it. Cover with plastic wrap; chill until firm, about 1 hour.
• Place cake, seam side down, on a serving platter; tuck parchment around it to keep platter clean while decorating.
• Whip ganache at medium speed until it has the consistency of soft butter. Cut two wedges off ends of cake at a 45-degree angle; set aside. Ice log with a thin layer of ganache. Attach wedges on diagonally opposite sides of log. Spread ganache all over log, using a small spatula to form barklike ridges. Chill until ganache is firm, about 30 minutes.
• In the top of a double boiler or in a heatproof bowl set over simmering water, melt chocolate until smooth. Line a baking sheet with parchment. Spread melted chocolate 1/8 inch thick over parchment. Refrigerate until cold, 10 to 15 minutes. Roll paper back and forth until chocolate splinters; sprinkle over cake. Chill cake until ready to serve.
• When ready to serve, arrange meringue mushrooms around and on cake, and dust lightly with confectioners' sugar.

WHITE CHOCOLATE MOUSSE

Steps:

• Dissolve gelatin in 1/4 cup cold water; let stand 5 minutes. Place chocolate in the bowl of a food processor and pulse until very finely chopped.
• Prepare an ice-water bath. Place 3/4 cup cream in a small saucepan, and bring to a simmer over medium-high heat. Add gelatin mixture and stir until completely dissolved, 30 seconds. Pour into food processor with motor running and process until chocolate mixture is smooth.
• Transfer to a medium bowl and place over ice water bath. Chill until mixture is thick enough to fall from a spoon in ribbons.
• Meanwhile, whip remaining 1 3/4 cups cream to soft peaks. Fold into chilled chocolate mixture. If not using immediately, refrigerate in an airtight container up to 1 day.

BûCHE DE NOëL

Steps:

• Mushrooms and buttercream:
• Preheat oven to 225°F. Whisk egg whites, sugar, cream of tartar, and salt in a large heatproof bowl set over a medium saucepan of simmering water (bowl should not touch water) until egg whites are very liquid (mixture will be warm to the touch) and sugar is dissolved (rub between your fingers to check), about 5 minutes. Remove bowl from heat and beat with an electric mixer until stiff, glossy peaks form (bowl will feel cool), about 5 minutes.
• Line a rimmed baking sheet with parchment paper and dust very lightly with cocoa powder. Scoop out 1 cup meringue. Dollop heaping teaspoonfuls of meringue onto prepared baking sheet, spacing at least 1 1/2" apart.
• Lightly dust meringue with more cocoa powder and place a sheet of parchment over top. Use an offset spatula or your hands to flatten meringue into irregularly shaped disks about 1/8" thick. Bake until lightly browned and parchment peels away easily, 75-90 minutes (meringue will be soft when it first comes out of the oven but will dry and crisp as it cools).
• Meanwhile, with mixer on medium speed, beat butter into remaining meringue, adding a piece at a time and waiting until incorporated before adding more. Beat until mixture is very smooth. (If it looks very loose or curdled, just keep beating; buttercream will come back together.) Add vanilla extract and scrape in vanilla seeds; beat to combine.
• Do Ahead
• Mushrooms and buttercream can be made 2 days ahead. Store mushrooms airtight at room temperature. Cover and chill buttercream; bring to room temperature, then beat until smooth before using.
• Sponge Cake:
• Increase oven to 400°F. Coat a 26x18" rimmed baking sheet with nonstick spray and line with parchment paper, leaving overhang on long sides. Spray parchment. Whisk flour, cornstarch, and ⅓ cup cocoa powder in a small bowl.
• Bring milk, butter, oil, vanilla, and salt to a simmer in a small saucepan over medium-low heat. Keep warm over low heat.
• Meanwhile, beat eggs and egg yolks with an electric mixer on medium speed until smooth. Increase speed to high; beat until doubled in volume. With motor running, gradually add sugar; beat until very light and fluffy and mixture falls back on itself in a slowly dissolving ribbon (it should be at least quadrupled in volume), about 5 minutes.
• Reduce speed to medium and gradually stream in milk mixture. Sift one-third of dry ingredients over top; gently fold in until only a few streaks remain. Working in 2 additions, repeat with remaining dry ingredients, scraping bottom of bowl and using as few strokes as possible to keep eggs from deflating (a few streaks are fine). Scrape batter into prepared baking sheet and gently spread to edges of pan. Tap sheet lightly on counter to pop any large air bubbles.
• Bake cake until surface is puffed and springy to the touch, 10-12 minutes.
• Let cake cool in pan 2 minutes, then run a knife along short edges to loosen. Invert onto a wire rack and carefully peel away parchment. Using a fine-mesh sieve, dust cake with cocoa powder. Cover with a large kitchen towel. Place another wire rack on top and flip cake over so towel side is underneath. Remove top rack; dust exposed side with cocoa powder. Starting at one of the long sides, gently roll up warm cake inside towel. Let cake cool, seam side down, 30-35 minutes.
• Do Ahead
• Cake can be baked 1 day ahead. Store tightly wrapped in plastic at room temperature.
• Assembly:
• Carefully unroll towel and cake on a flat surface (cake will curl at the ends and may have a few small cracks but should stay in 1 piece). Position cake so the end that was in innermost part of spiral is closest to you; brush off any excess cocoa.
• Using a pastry brush, gently dab cocoa syrup over entire surface of cake; you may not use it all. Dollop bittersweet ganache over top and smooth with an offset spatula to create an even layer.
• Dollop mascarpone filling over ganache; carefully spread over surface, trying not to blend with ganache and avoiding last inch of cake along long side farthest from you.
• Using towel to lift edge nearest you, reroll cake, keeping towel on exterior. Chill, seam side down, until filling is set, about 30 minutes.
• Transfer filled cake to a baking sheet. Set aside 1/2 cup buttercream for attaching branches. Evenly spread remaining buttercream over cake with an offset spatula.
• Using a long serrated knife, trim 1/2" of cake from each end to create clean edges; discard (or eat!). Slice off a 4" piece of cake. Starting 1" from end, divide 4" piece in half, cutting at a 45° angle, leaving 1" at opposite end. Transfer log to a platter.
• Place angled side of each small piece of cake against roll to create branches, positioning one on top and the other on the side using a large dab of buttercream to secure. Cover any exposed cake on sides with more buttercream but leave cut ends exposed.
• Use spatula to create textured lines in buttercream to look like birch bark.
• Knead together marzipan and cocoa powder on a surface until smooth. Roll out on a sheet of parchment paper to less than 1/8" thick, then cut out wavy strips to look like tree knots; drape over buttercream and press gently to adhere.
• Using either a pastry bag fitted with a very small round tip or a disposable plastic bag with one corner snipped off, drizzle melted chocolate over log to mimic birch bark striations. Chill Bûche de Noël, uncovered, until ready to serve.
• Just before serving, press mushrooms perpendicularly into log in groups of 2 or 3.
• Do Ahead
• Bûche de Noël (without meringue mushrooms) can be assembled 1 day ahead. Wrap in plastic and chill. Attach mushrooms just before serving.