Chocolate Mayonnaise Cake

Preparation

1. cake

   Step 1

   Preheat oven to 350°F. Butter and flour three 8-inch-diameter cake pans with 1 1/2-inch-high sides. Combine chopped chocolate and cocoa powder in medium metal bowl. Add 13/4 cups boiling water and whisk until chocolate is melted and mixture is smooth.

   Step 2

   Sift flour, baking soda, and baking powder into another medium bowl. Using electric mixer, beat both sugars and mayonnaise in large bowl until well blended, 2 to 3 minutes. Add eggs 1 at a time, beating until well blended after each addition. Beat in vanilla. Add flour mixture in 4 additions alternately with chocolate mixture in 3 additions, beating until blended after each addition and occasionally scraping down sides of bowl. Divide batter among prepared cake pans (about 2 1/3 cups for each).

   Step 3

   Bake cakes until tester inserted into center comes out clean, 30 to 32 minutes. Cool cakes in pans on racks 20 minutes.

   Step 4

   Run small knife around sides of cakes to loosen. Carefully invert cakes onto racks and let cool completely.

2. FROSTING

   Step 5

   Place chopped chocolate in medium metal bowl; set bowl over saucepan of simmering water and stir until chocolate is melted and smooth. Carefully remove bowl from over water; let melted chocolate cool until lukewarm, stirring occasionally.

   Step 6

   Using electric mixer, beat butter in large bowl until smooth and creamy. Sift powdered sugar over butter and beat until well blended, about 2 minutes. Beat in vanilla. Add melted chocolate and beat until well blended and smooth, occasionally scraping down sides of bowl.

   Step 7

   Place 1 cake layer on platter. Spread 3/4 cup frosting over top of cake layer to edges. Top with second cake layer; spread 3/4 cup frosting over. Top with third cake layer. Spread remaining frosting decoratively over top and sides of cake. DO AHEAD Can be made 1 day ahead. Cover with cake dome and let stand at room temperature.

   Step 8

   Cut cake into wedges and serve.