For the cake:
- Butter for greasing baking pans
- 1 ½ cups all-purpose flour
- 1 cup of sugar
- 1 teaspoon baking powder
- ½ teaspoon baking soda
- ⅓ cup best-quality cocoa powder
- 6 ounces (1 ½ stick) unsalted butter, at room temperature
- 2 large eggs, at room temperature
- 2 teaspoons vanilla
- ¾ cup sour cream, at room temperature
For the frosting:
- 6 ounces good-quality semisweet chocolate, broken into small pieces
- 3 ounces ( ¾ stick) unsalted butter
- 1 tablespoon light corn syrup
- ½ cup sour cream
- 1 teaspoon vanilla
- 2 ½ cups confectioners’ sugar, sifted
- For cake:
heat oven to 350 degrees. Butter sides of two 8-inch cake pans, and line bottoms with parchment paper. In the bowl of a food processor fitted with a knife blade, combine flour, sugar, baking powder, baking soda, cocoa powder, butter, eggs, vanilla, and sour cream. The process to make a smooth, thick batter.
- Using a rubber spatula, divide the batter between pans, and smooth tops. Bake until a cake tester inserted in center comes out clean, 25 to 35 minutes; do not overbake. Transfer to a wire rack to cool for 10 minutes before removing from cake pans.
- For frosting:
Combine chocolate and butter in a large heat-proof bowl, and heat until melted in a microwave oven or over a pan of simmering water. Remove from heat, and allow to cool for 5 minutes. Stir in corn syrup, sour cream, and vanilla. Whisk in confectioners’ sugar until very smooth. Frosting should be thick and spreadable. If necessary, add a teaspoon or two of boiling water to thin it, or additional sifted confectioners’ sugar to thicken.
- Cut four strips of waxed or parchment paper, and place them side by side on a cake plate, covering the surface. Place one cake layer domed-side down on a plate.
- Spoon about a third of the frosting onto the center of the cake, and use a knife or a spatula to spread it evenly. Place the other cake on top, domed side up. Spoon another third of the frosting on top of the cake, spreading to make swirls or a smooth finish. Spread sides of the cake with remaining frosting, and allow to sit for a few minutes until set. Carefully remove paper strips. Place cake under glass or in an airtight container, and set aside in a cool place until serving.