Chocolate Mayonnaise Cake

Chocolate Mayonnaise Cake
10-12 servings
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2 ounces bittersweet chocolate (do not exceed 61% cacao), chopped
2/3 cup unsweetened cocoa powder
1 3/4 cups boiling water
2 3/4 cups all-purpose flour
1 1/4 teaspoons baking soda
1/4 teaspoon baking powder
1 cup sugar
1 cup (packed dark brown sugar
1 1/3 cups mayonnaise- Hellmann's (do not use reduced fat-low or no fat)
2 large eggs
1 teaspoon vanilla extract

10-ounces bittersweet chocolate (do not exceed 61% cacao), chopped
1 1/2 cups (3 sticks) butter, room temperature
3 cups powdered sugar, sifted (measured, then sifted)
1 tablespoon vanilla extract

Special equipment
3 8-inch-diameter cake pans with 1 1/2-inch sides

Preheat oven to 350 degrees F. Butter and flour three 8-inch round cake pans with 1 1/2-inch high sides. Combine chocolate and cocoa powder in medium metal bowl. Add 1 3/4 cups boiling water and whisk until chocolate is melted and mixture is smooth. This is called blooming. Set aside to cool.

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 pan).

Bake cakes until tester inserted into center comes out clean, 30 to 32 minutes. Cool cakes in pans on rack 20 minutes. Run small knife around sides of cake to loosen. Invert cakes onto racks and cool completely.

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

Using electric mixer, beat butter in large bowl until smooth and creamy. Add powdered sugar 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.

Place one layer on platter. Spread 3/4 cup frosting over top of cake layer to edges. Top with second layer; spread 3/4 cup frosting over. Top with third layer. Spread remaining frosting decoratively over top and sides of cake. Cut and serve.

Do ahead: Can be made 1 day ahead. Cover with cake dome and let stand at room temperature. I think it is better if you allow to stand overnight.