Instructions

1. Place 12 large egg whites (about 1 2/3 cups) in the bowl of a stand mixer fitted with the whisk attachment and let sit until room temperature. Arrange a rack in the middle of the oven, remove any racks above it, and heat the oven to 350°F.
2. Sift 3/4 cup cake flour, 1/4 cup Dutch process cocoa powder, and 3/4 teaspoon espresso powder if desired into a medium bowl. Add 1 cup of the granulated sugar and 1/2 teaspoon kosher salt and whisk to combine.
3. Beat the egg whites on medium speed until foamy, about 1 minute. Add 1 1/4 teaspoons cream of tartar and 2 teaspoons vanilla extract and beat until soft peaks form, about 1 minute.
4. With the mixer on medium speed, beat in the remaining 2/3 cup granulated sugar one tablespoon at a time until incorporated. Continue beating until stiff, moist, glossy peaks form that flop just a bit at the top when the whisk is turned upside down, 5 to 10 minutes total.
5. Remove the bowl from the mixer. Sift a third of the flour mixture over the whites and gently fold in with a flexible spatula. Repeat with sifting and folding in the flour mixture in two more additions. If your sifter is super fine, the sugar may not pass through it — just add any unsifted sugar into the bowl.
6. Transfer the batter to an ungreased 10 to 12 cup tube pan, preferably with legs. Run a small offset spatula or butter knife through the batter to break up any air bubbles and smooth the top. Bake until the top of the cake is dry and a cake tester inserted into the center comes out with a moist crumb or two, 30 to 35 minutes.
7. If the pan has legs, place upside down on a heatproof surface. If the pan does not have legs, flip the pan over and position the tube onto the neck of a wine bottle. Let the cake cool completely upside down, about 1 1/2 hours. Run a thin knife around the sides of the pan and the tube to release the cake. Invert the cake onto a serving plate and remove the pan.
8. Place 4 cups cold heavy cream in the clean bowl of a stand mixer fitted with the whisk attachment. Beat on medium to medium-high speed until the cream begins to thicken, about 1 minute. Add 2/3 cup powdered sugar, 1/2 cup Dutch process cocoa powder, 1 tablespoon vanilla extract, and 1/2 teaspoon kosher salt, and continue beating until medium peaks form, about 2 1/2 minutes.
9. Using a large serrated knife and a sawing motion, gently slice the cooled cake in half horizontally. Remove the top half. Spread about 1/4 of the whipped cream onto the cut side of the bottom half. Place the top layer on the whipped cream cut-side down. Decoratively spread the remaining whipped cream over the sides and top of the cake. Dust with cocoa powder and refrigerate for 30 minutes.
10. Using a serrated knife, slice the cake. Serve slices with an additional dusting of cocoa powder and a few mixed berries.