MUSHROOM-BACON GALETTE

Steps:

• Crust:Pulse flour, sugar, and salt in a food processor until combined. Add butter and pulse until mixture resembles coarse meal and there are some small flake-size pieces and some larger pea-size pieces. Add a little of the ice water and pulse; add some more and pulse; continue until all the water is in. Now work in longer pulses, stopping to scrape sides and bottom of bowl if needed, until dough forms bumpy curds that hold together when pinched.
• Turn dough out onto a clean work surface and gently knead to bring it together. Gather into a ball, flatten into a disk, and place between two large sheets of parchment. Roll out dough to a 12-inch circle. Slide dough, still between sheets of parchment, onto a baking sheet or cutting board and refrigerate at least 2 hours or, well wrapped, up to 3 days. (Dough can also be frozen, well wrapped, up to 2 months.)
• When you're ready to use the dough, let stand on counter for a few minutes, until it's pliable enough to lift and fold without cracking.
• Filling:Place bacon in a heavy skillet and cook over medium heat, turning occasionally, until crispy and golden brown on both sides. Transfer to a paper towel-lined plate, pat dry with more paper towels, and let cool completely. Finely chop bacon or cut into slender strips. Pour off all but 1 tablespoon fat from skillet; set skillet aside.
• Preheat oven to 400 degrees with rack in center.
• Pour oil into skillet with bacon fat and heat over medium. Add mushrooms, leeks or onion, and garlic; season lightly with salt. Cook, stirring, until vegetables are softened, about 5 minutes. (Mushrooms will release liquid, and then, as you continue to cook, take it up again.) Add wine and cook, stirring and scraping bottom of skillet, until it evaporates, 1 to 2 minutes. Pour in cream and cook, stirring, until mostly absorbed. Remove from heat; stir in bacon, pepper (to taste), walnuts, 2 tablespoons cheese, and thyme. (Filling can be made ahead and refrigerated, covered, up to 3 days.)
• Peel top sheet of parchment off dough; leave dough on bottom sheet of parchment and keep on baking sheet. Scrape filling onto dough; using a spatula, spread into a 9-inch circle. Lift the bare border of dough and fold over filling. As you fold, dough will pleat on itself (don't worry about being neat or getting everything even). (Galette can be made up to this point and refrigerated for a few hours before baking; bake straight from refrigerator.)
• Bake until crust is deeply golden and filling is hot, 30 to 35 minutes. Transfer sheet to a wire rack and sprinkle remaining 2 tablespoons cheese over the filling, and if desired, the crust. Drizzle with oil, if desired. Let cool about 10 minutes or let cool to room temperature, then cut with a pizza wheel and serve. Galette is best served within a few hours of baking.