Chocolate Sour Cream Cake with Chocolate Buttercream Frosting Ingredients For the Chocolate Sour Cream Cake: 3/4 cup sour cream, at room temperature 1/2 cup plus 3 tablespoons cocoa powder 2 large eggs, at room temperature 2 large egg yolks, at room temperature 1 1/2 teaspoons pure vanilla extract 2 1/4 cups cake flour 1