- 3/4 cup unsweetened cocoa powder
- 1/4 cup (1/2 stick) unsalted butter, room temperature
- 2/3 cup (packed) dark brown sugar
- 1/2 cup plus 2 tablespoons buttermilk
- Chocolate-Chocolate Chip Cream Frosting (see recipe)
- White chocolate shavings and bittersweet (not unsweetened) or semisweet chocolate shavings
Preheat oven to 350°F. Butter and flour sides of two 8-inch-diameter cake pans with 1 1/2-inch-high sides. Line bottoms of pans with parchment paper; butter and flour parchment. Sift cake flour, baking soda and salt into medium bowl. Stir cocoa and 1/2 cup water in large bowl until very thick paste forms. Set aside.
Beat unsalted butter, sugar and brown sugar in another medium bowl until well blended. Add eggs 1 at a time, beating well after each addition. Gradually add egg mixture to cocoa mixture, beating until mixture is smooth. Beat in dry ingredients alternately with buttermilk in 2 additions each, beating well after each addition.
Divide batter between prepared pans. Bake until tester inserted into center of cakes comes out clean, about 30 minutes. Cool cakes in pans on rack 15 minutes. Turn cakes out onto racks; peel off parchment. Cool completely. DO AHEAD Can be prepared 1 day ahead. Wrap in plastic and store at room temperature.
Using serrated knife, cut each cake horizontally in half (layers will be thin). Using 9-inch tart pan bottom as aid, transfer 1 cake layer, cut side up, to platter. Spread generous 1/2 cup Chocolate- Chocolate Chip Cream Frosting over. Repeat layering 2 more times, using 1 cake layer and generous 1/2 cup frosting for each layer. Top with fourth cake layer, cut side down. Spread remaining frosting over top and sides of cake. Sprinkle top with white and bittersweet chocolate shavings. Chill at least 1 hour and up to 6 hours. Slice cake.