Triple-Chocolate Layer Cake

8 to 10 servings

CAKE
1 cup cold buttermilk
1 tablespoon instant espresso powder
2 teaspoons vanilla extract

1-1/4 cups sugar
1 cup cake flour
6 tablespoons unsweetened cocoa powder (preferably Dutch-process)
1/2 teaspoon salt
1/4 teaspoon baking powder
1/4 teaspoon baking soda
3 large eggs
1/2 cup (1 stick) unsalted butter, room temperature

FILLNG AND FROSTING

4 ounces good-quality white chocolate (such as Baker's or Lindt), finely chopped
4 ounces imported milk chocolate, finely chopped
1 cup plus 1 tablespoon chilled whipping cream
6 ounces bittersweet (not unsweetened) or semisweet chocolate, finely chopped white and milk chocolate shavings (optional)

FOR CAKE: Preheat oven to 350 degrees. Butter three 8-inch-diameter cake pans with 1-1/2 inch high sides. Line bottom of pans with parchment paper. Stir buttermilk, espresso powder and vanilla in small bowl until powder dissolves.

Sift sugar and next 5 ingredients into large bowl. Add eggs and butter; heat until mixture is thick and smooth, about 1-1/2 minutes. Add buttermilk mixture; beat until light and fluffy, about 1-1/2 minutes longer. Divide batter among pans.

Bake cakes until tester inserted into center comes out clean, about 20 minutes. Cool cakes in pans on racks 5 minutes. Turn cakes out onto racks. Peel off parchment; cool completely.

FOR FILLINGS AND FROSTING: Place white chocolate and milk chocolate in separate medium bowls. Bring 1 cup cream to boil in heavy medium saucepan. Pour 3 tablespoons hot cream into white chocolate and 3 tablespoons hot cream into milk chocolate. Add bittersweet chocolate to remaining cream in saucepan; stir until smooth. Stir white chocolate and milk chocolate fillings until smooth; chill until cold but not firm, about 15 minutes. Set aside bittersweet chocolate frosting.

Place 1 cake layer on platter. Using handheld mixer. beat white chocolate filling until slightly stiff. Spread over cake layer. Top with second cake layer. Add remaining 1 tablespoon cream to milk chocolate filling and beat until smooth. Spread over second cake layer. Top with third cake layer: Chill cake until bittersweet chocolate frosting is firm enough to spread, about 30 minutes.

Stir frosting until smooth. Spread very thin layer over top and sides of cake to smooth surface and anchor crumbs. Chill 30 minutes. Spread remaining frosting decoratively over cake. (Can be made 1 day ahead. Cover with cake dome and chill.)

Garnish cake with chocolate shavings, if desired, and serve.