For the Cake:
2 1/3 cups all-purpose flour
1 cup unsweetened cocoa powder, sifted
1 1/2 tsp. baking powder
1/2 tsp. baking soda
1/2 tsp. salt
12 tbsp. (1 1/2 sticks/6 oz./170g) unsalted butter, at room temperature
2 cups firmly packed light brown sugar
2 tsp. vanilla extract
4 eggs, at room temperature
1 1/2 cups buttermilk, at room temperature
For the Frosting:
12 oz. bittersweet chocolate, finely chopped
1 3/4 cups heavy cream
1/2 cup sour cream
Pinch of salt
For the Cake:
Preheat oven to 350 degrees F/180 degrees C. Lightly butter the bottoms of two round 9 x 2-inch cake pans and line with parchment paper. Lightly butter the paper and the sides of the pans and dust with flour.
In a large bowl, sift together the flour, cocoa powder, baking powder, baking soda and salt; set aside.
In another large bowl, using an electric mixer, beat the butter on medium speed until smooth. Gradually add the brown sugar and continue beating until fluffy. Beat in the vanilla. Add the eggs one at a time, beating well after each addition.
Reduce the speed to low and add the flour mixture in three additions, alternating with the buttermilk and beginning and ending with the flour, beating after each addition.
Divide the batter between the prepared pans and spread it out evenly. Tap the pans gently on the counter to dispel air pockets. Bake until a toothpick inserted into the center of a cake comes out clean, 25 to 30 minutes. Transfer the pans to a wire rack and let cool for 15 minutes. Run a small knife around the inside of each pan to loosen the cakes. Invert onto the rack and lift off the pans, then carefully peel off the parchment paper. Let the cake layers cool completely before frosting.
To Make the Frosting:
In the top pan of a double boiler, combine the chocolate and heavy cream. Set the pan over but not touching barely simmering water in the bottom pan and melt the chocolate, then whisk until well blended. Let cool slightly. Add the sour cream and salt and stir just until blended. Let cool to room temperature, stirring occasionally. Whisk the frosting briefly until lighter in color and thick enough to spread.
Brush away any loose crumbs from both cake layers. Place one layer, top side down, on a flat serving plate. With an icing spatula, spread about one-third of the frosting evenly on top. Place the other layer, top side down, on the first layer and press gently. Spread a thin layer of frosting over the entire cake to seal in any crumbs, then thickly coat the cake with the remaining frosting. Serve immediately or keep covered at room temperature until ready to serve.
Makes one 9-inch layer cake; serves 10 to 12.
Date: May 14, 2007