Cake
2 cups cake flour (1 3/4 cup AP flour plus 1/4 cup cornstarch)
3/4 cup natural unsweetened cocoa powder
1 1/2 tsp baking soda
3/4 tsp salt
3/4 cup (1 1/2 sticks) unsalted butter, room temperature< 2 cups (packed) brown sugar 3 large eggs 1 1/2 tsp vanilla extract 1 cup buttermilk 4 tsp instant espresso powder dissolved in 3/4 cup hot water (strong instant coffee will do) Frosting
1/3 cup natural unsweetened cocoa powder
1 Tbs instant espresso powder (instant coffee will do, but grind it more finely)
1 1/2 cups chilled heavy whipping cream, divided
1 1/3 cups sugar
16 oz chilled mascarpone cheese
For the Cake:
- Position rack in the center of the oven; preheat to 325 degrees. Generously butter two 9-inch cake pans; dust with flour; line bottom with parchment paper.
- Sift cake flour, cocoa, baking soda, and salt into medium bowl. Cream butter and sugar in stand mixer. Add eggs one at a time, beating well after each. Mix in vanilla. Add flour in 3 additions, alternating with 2 additions of buttermilk, beating until just blended after each. Gradually add hot espresso, beating just until smooth.
- Divide batter into pans and smooth tops. Bake until tester comes out clean, 40 minutes. Cool cakes for 15, then invert onto racks and remove parchment. Invert again so top side is up. Cool completely.
For the Frosting:
- Sift cocoa into large bowl with espresso powder. Bring 1 cup cream to a boil, and then slowly pour over cocoa mixture, whisking until dissolved. Add sugar and 1/2 cup cream; stir until sugar dissolves. Chill 2 hours.
- Add mascarpone to chilled cocoa mixture. Beat on low speed until smooth. Increase speed to high, beat until thickened and medium-firm peaks form. Do not over beat.
- Brush crumbs off of cakes. Place one cake layer on platter, spread 1 3/4 cup frosting to edges. Top with second layer, press to adhere. Spread thin layer of frosting over top and sides. Chill 10 minutes. Spread remaining frosting over top and sides. Chill.
