Roulades are a classic sponge cake-based dessert that is also called "jelly roll" in the United States and "Swiss roll" in Britain. Try this delicious version from chef Michel Roux's "Desserts."
Preheat oven to 425 degrees. Line a rimmed baking sheet with parchment paper; butter and flour parchment paper and set aside.
In the bowl of an electric mixer fitted with the whisk attachment, beat yolks and scant 1 cup confectioners' sugar in a bowl until ribbons form; set aside. In the clean bowl of an electric mixer fitted with the whisk attachment, whisk egg whites until they reach soft peaks; add a scant 1/2 cup confectioners' sugar and continue whisking until stiff peaks form.
Whisk in one-third of the yolk mixture into the egg white mixture; fold in remaining yolk mixture using a metal spoon until it is almost fully incorporated. Sift cocoa and potato flour into bowl; gently fold with a metal spoon until just combined.
Using an offset spatula, spread batter on prepared baking sheet to form a 10 1/2-by-12-inch rectangle, about 5/8 inch thick. Transfer to oven and bake until cake springs back when touched, 8 to 10 minutes.
Meanwhile, line a large wire rack with a clean dish towel. Turn cake out onto prepared rack and carefully peel off parchment paper. Let stand 5 minutes to cool.
Meanwhile, in the bowl of an electric mixer fitted with the whisk attachment, beat heavy cream with remaining 1/4 cup confectioners' sugar until ribbons form; set aside.
Carefully transfer cake to a large piece of wax paper. Using a pastry brush, brush 1/4 cup coulis over cake; using a serrated knife, carefully trim edges from all four sides. Using an offset spatula, spread cream over cake, leaving a 5/8-inch border all around; top with raspberries. Starting from one of the long sides, gently roll up cake, using the wax paper to help you. Transfer cake to refrigerator and let chill 2 to 3 hours.
Slice roulade crosswise and serve dusted with confectioners' sugar and drizzled with coulis.