Coffee infuses this soaring confection's layers (separated by a rich mascarpone filling) as well as its whipped-cream coating. The chocolate feathers are made with melted white, milk, dark, and milk plus white chocolate for a café-au-lait color. This recipe comes from Martha Stewart’s Cake Perfection: 100+ Recipes for the Sweet Classic, From Simple to Stunning (Clarkson Potter).
Cake: Preheat oven to 325°F. In a large bowl, whisk together flour, 3/4 cup granulated sugar, baking powder, and salt. Add coffee, oil, egg yolks, and vanilla; whisk until smooth. Beat egg whites on medium speed until frothy, about 2 minutes. Increase speed to medium-high and gradually add remaining 3/4 cup granulated sugar; beat until stiff, glossy peaks form, about 5 minutes. Gently fold one-third of whites into batter, then fold in remaining whites.
Divide batter evenly among three ungreased 8-inch round pans, smoothing tops with an offset spatula. Bake until lightly golden and tops spring back when gently pressed, 25 to 30 minutes. Transfer pans to wire racks; let cool 15 minutes. Run a small offset spatula around edges and turn out cakes, upside-down, onto racks; let cool completely. With a serrated knife, split each cake in half horizontally (making 6 layers).
Filling: Beat mascarpone with salt on low speed until combined. With mixer running, slowly add cream. Increase speed to medium; gradually add confectioners' sugar and beat to medium peaks. Refrigerate, covered, until ready to use.
Feathers: Melt each chocolate in a separate heatproof bowl set over (not in) a pan of simmering water, stirring until smooth. Mix a little melted milk chocolate into half of melted white chocolate to create a fourth color.
Working in batches, spoon half-dollar-size pools of melted chocolate onto baking sheets lined with nonstick baking mats or parchment. (If chocolate hardens as you're working, reheat over simmering water.) Using pastry brushes and short, quick strokes, brush melted chocolate into feather shapes. Refrigerate until set, at least 30 minutes.
Coffee whipped cream: Beat granulated sugar, salt, cream, and coffee on medium-low speed until sugar has dissolved, about 1 minute. Increase speed to medium-high and beat to stiff peaks, about 3 minutes. (For a stronger coffee flavor, whisk in another 1 to 2 tablespoons coffee.)
Anchor one cake layer, bottom-side down, on an 8-inch board with a dab of whipped cream. Spread 3/4 cup mascarpone filling evenly over layer, then top with a second cake layer. Spread evenly with 3/4 cup whipped cream, then repeat process, alternating filling and whipped cream between layers, and ending with sixth and final cake layer, bottom-side up.
Spread a thin layer of whipped cream over cake to form a crumb coat; refrigerate until firm, about 15 minutes. Spread all but 1/4 cup of remaining whipped cream over top and sides of cake. Create a layering effect with chocolate feathers by attaching them, at a slight angle, to side of cake with dabs of remaining whipped cream to anchor.
Recipe reprinted from: Martha Stewart’s Cookie Perfection: 100+ Recipes to Take Your Treats to the Next Level, From the Kitchens of Martha Stewart Living. Copyright © 2020 by Martha Stewart Living Omnimedia, Inc. Published by Clarkson Potter/Publishers, an imprint of Random House, a division of Penguin Random House LLC. Available October 13th wherever books are sold; to pre-order, go to amazon.com.