Credit NYT cooking FOR THE CAKE: Butter for greasing baking pans 1 1/2 cups all-purpose flour 1 cup sugar 1 teaspoon baking powder 1/2 teaspoon baking soda 1/3 cup best-quality cocoa powder 6 ounces (1 1/2 sticks) unsalted butter, at room temperature 2 large eggs, at room temperature 2 teaspoons vanilla 3/4 cup sour cream, at room temperature FOR THE FROSTING: 6 ounces good-quality semisweet chocolate, broken into small pieces 3 ounces ( 3/4 stick) unsalted butter 1 tablespoon light corn syrup 1/2 cup sour cream 1 teaspoon vanilla 2 1/2 cups confectioners' sugar, sifted Step 1 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. Process to make a smooth, thick batter. Step 2 Using a rubber spatula, divide batter between pans, and smooth tops. Bake until a cake