DOUBLE CHOCOLATE CAKE

Steps:

• Cake: Preheat oven to 350 degrees Fahrenheit. Butter two 9-inch cake pans with 1 1/2 inch high sides. Dust with powdered sugar. Line pan bottoms with parchment paper rounds. Sift flour, baking soda, and salt into medium bowl. Whisk 1 cup powdered sugar, 1/2 cup buttermilk, and cocoa powder in another medium bowl until smooth. Whisk remaining 1/2 cup buttermilk and vanilla in small bowl. Using electric mixer, beat butter in large bowl until creamy. Add remaining 1 cup powdered sugar; beat until smooth. Add eggs 1 at a time, beating to blend after each addition. Beat in cocoa mixture. Add flour mixture in 3 additions alternately with vanilla-buttermilk mixture in 2 additions, beating to blend after each addition. Divide batter between prepared pans. Bake until tester inserted into centers comes out clean, about 25 minutes. Cool 10 minutes in pans on rack. Invert cakes onto rack and cool completely. DO AHEAD Can be made 1 day ahead. Cover and store at room temperature. Icing: Bring 3/4 cup water and sugar to boil in small saucepan, stirring until sugar dissolves. Boil until syrup is reduced to 3/4 cup, about 2 minutes. Cool. Using electric mixer, beat butter in medium bowl until smooth. Beat in sour cream and vanilla. Gradually beat in powdered sugar and cocoa powder, then 1/2 cup milk. Cut cakes horizontally in half. Place 1 cake layer on plate. Brush with 3 tablespoons syrup. Spread 1/2 cup icing over. Place second cake layer atop icing. Repeat sequence 2 more times. Brush top layer with remaining 3 tablespoons syrup. Cover top and sides of cake with remaining icing. DO AHEAD Can be made 2 days ahead. Cover with cake dome and chill. Let stand 1 hour at room temperature bfore serving. Cut into slices and serve.