ORANGE-WALNUT BUCHE DE NOEL

Steps:

• Preheat oven to 300 degrees. Coat a 12-by-17-inch rimmed baking sheet with cooking spray. Line with parchment paper. Spray and flour parchment, tapping off excess; set aside. In a food processor, pulse walnuts and flour until coarsely ground; set aside.
• In the bowl of an electric mixer, whisk egg yolks with 5 tablespoons sugar until thick and pale. Beat in vanilla. In a clean mixing bowl fitted with a clean whisk, beat egg whites with salt until soft peaks form. Gradually add remaining 5 tablespoons sugar, beating until stiff (but not dry) glossy peaks form. Fold egg whites into yolk mixture in 3 equal batches, and add walnut mixture with last batch.
• Spread batter evenly on prepared baking sheet. Bake until top is golden and springs back when touched, about 30 minutes. Run a small, sharp knife around edges of cake; invert cake onto a clean kitchen towel dusted with confectioners' sugar. Peel off parchment paper. Starting at a short side, gently roll the cake into a log, incorporating towel. Transfer to a wire rack, and let cool completely, about 1 hour.
• Reserve 1 1/2 cups mascarpone filling. Unroll cake and spread remaining filling on top, leaving a 1/2-inch border on all sides. Carefully reroll cake (without towel). Arrange, seam-side down, on a parchment-lined baking sheet. Using a serrated knife, trim ends of log. Spread reserved filling over log. Working quickly, arrange chocolate bark all over log, overlapping pieces slightly. Refrigerate until firm, at least 1 hour. Garnish with acorns and leaves, if desired; dust with confectioners' sugar before serving.