Ingredients
- 1 2/3 cups all purpose flour
- 3/4 cup unsweetened natural cocoa powder
- 2 teaspoons baking powder
- 1 teaspoon baking soda
- 1 teaspoon salt
- 1/2 cup toasted, finely chopped walnuts
- 2 cups sugar
- 12 tablespoons unsalted butter, room temperature
- 2 teaspoons vanilla extract
- 2 eggs
- 2 cups buttermilk
- Frosting
- 10 ounces bittersweet chocolate
- 4 tablespoons unsalted butter, room temperature
- 1/2 cup powdered sugar
- 1 teaspoon vanilla extract
- 1/4 teaspoon salt
- 3/4 cup sour cream
- 1 1/2 cups toasted walnuts, coarsely chopped
The Steps
1. Position rack in the center of the oven and preheat to 350°F. Butter 2 9-inch round cake pans. Line pans with parchment; butter and flour parchment. Sift flour, cocoa powder, baking powder, baking soda and salt into a medium bowl.
2. Using an electric mixer, beat the sugar, butter and vanilla until very light and fluffy. Beat in eggs, one at a time. Mix the dry ingredients and the buttermilk into the batter, beginning and ending with the dry ingredients, just until combined. Stir in the walnuts.
3. Transfer the batter to the prepared pans, dividing evenly; smooth tops. Sprinkle 1/4 cup of the pecans over the surface of the batter. Bake until a tester inserted in the center of the cakes comes out clean, about 30 minutes. Cool the cakes 10 minutes on racks. Run a knife around the edge of the cakes and turn cakes out onto racks. Cool cakes completely.
4. For Frosting: Melt the chocolate in a heavy small saucepan, stirring constantly over low heat until smooth. Let the chocolate stand until just cool to touch, about 20 minutes.
5. Using an electric mixer, beat the butter in a medium bowl until smooth Add the powdered sugar, vanilla and salt and beat until fluffly. Beat in the chocolate, then the sour cream. Place one layer on a cake plate. Spread 3/4 cup frosting over the layer and sprinkle with 3/4 cup walnuts; top with second cake layer. Spread the remaining frosting over the top and sides of cake. Sprinkle the top with the remaining walnuts. (Can be prepared 1 day ahead. Cover the cake with a cake dome and keep at cool room temperature.)
