BûCHE DE NOëL

Steps:

• Preheat the oven to 375°F.
• Line a 17 x 11 x 1-inch jelly roll pan with parchment paper. Brush it with melted butter, and dust it with flour.
• Prepare the cake:
• Sift the flour, baking powder and salt together onto a sheet of parchment paper. Beat the egg yolks and 3/4 cup of the sugar with the whisk attachment in an electric mixer until the mixture is thick and lemon colored. Add the dry ingredients at low speed, mixing until just incorporated. Add the vanilla, mix quickly and thoroughly, and set aside (the batter will be quite thick).
• In a separate bowl, whisk the egg whites with a pinch of salt until they form soft points. Add the remaining 1/4 cup of sugar and whisk until the egg whites are glossy and form points that stand up but are not too stiff. Fold one-fourth of the egg whites into the cake batter until they are incorporated, then fold in the remaining egg whites, working quickly. They should be incorporated into the batter, but do not overmix it.
• Spread the batter in the prepared pan, and bake until the cake is golden and your finger makes a slight indentation in the top of the cake when you press it, 8 to 10 minutes.
• While the cake is baking, sift the confectioner's sugar over a clean kitchen towel.
• Remove the cake from the oven, and immediately invert it onto the sugar-dusted towel. Peel the parchment paper from the cake, and starting from one long side, gently roll the cake up in the towel. Allow it to cool for 30 minutes.
• Make the frosting:
• Melt the chocolate and the cream together in a medium-sized, heavy saucepan over medium heat. Shake the pan occasionally, and when the chocolate has completely melted, whisk the mixture so it is completely combined. Let it cool to room temperature, so it is thick enough to spread. Transfer 3/4 cup of the chocolate mixture to a small bowl, and whisk in the chestnut purée. Season with vanilla if you like.
• When the cake has cooled, unroll it and trim off the edges so it is perfectly even, reserving the trimmings. Spread the filling evenly over the cake to within about 1/8-inch from the edges, and roll the cake back up. Roll the trimmings into spirals, and affix these to the sides of the cake with any leftover filling (usually two "knots" are sufficient!).
• Using the frosting, generously frost the cake, including the knots and the ends. Let the cake rest for about 15 minutes, then decorate it, first with the tines of a fork, then with the decorations of your choice. Let sit for at least 8 hours and up to 24 before servings.