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1
Preheat oven to 350u00b0.
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2
To prepare cake, combine 1 cup boiling water and 2/3 cup cocoa in a bowl, stirring until smooth. Add 2 ounces bittersweet chocolate; stir until smooth. Cool to room temperature. Coat 2 (8-inch) round metal cake pans with cooking spray; line bottoms of pans with wax paper. Coat wax paper with cooking spray; dust each pan with 1 teaspoon flour.
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3
Place 1 3/4 cups sugar, 6 tablespoons butter, and 1 teaspoon vanilla in a large bowl; beat with a mixer at medium speed 1 minute. Add egg whites, 1 at a time, beating well after each addition. Add sour cream; beat at medium speed 2 minutes. Weigh or lightly spoon 4 ounces flour (about 1 2/3 cups) into dry measuring cups; level with a knife. Combine 4 ounces flour, baking powder, baking soda, and 1/2 teaspoon salt in a bowl, stirring well. Add flour mixture and cocoa mixture alternately to sugar mixture, beginning and ending with flour mixture and beating just until combined.
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4
Divide batter evenly between prepared pans. Bake at 350u00b0 for 30 minutes or until a wooden pick inserted into center comes out clean. Cool in pans 10 minutes on wire racks. Invert cake layers onto racks; cool completely. Discard wax paper.
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5
To prepare filling, combine juice and next 6 ingredients (through 1/4 ounce bittersweet chocolate) in a small saucepan over low heat; bring mixture to a boil, stirring frequently. Cook 1 minute, stirring constantly. Pour into a bowl. Cover and chill. Uncover; fold in whipped topping.
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6
To prepare glaze, combine milk, 1 tablespoon butter, and 4 ounces bittersweet chocolate in a medium microwave-safe bowl; microwave at HIGH for 1 minute, stirring every 15 seconds until smooth.
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7
Place 1 cake layer on a plate. Spread filling over top, leaving a 1/4-inch border. Top with remaining cake layer. Spoon warm glaze over top of cake, allowing it to drip over the edges of cake.
