Chocolate Domingo Cake with Chocolate Egg White Buttercream

from ButterYum
serves 10-12
recipe adapted from The Cake Bible

1/4 cup plus 3 tablespoons (42g) Dutch processed cocoa powder
2/3 (160g) cup sour cream
2 large (100g) eggs
1 1/2 teaspoons (6g) pure vanilla extract
1 1/2 cups plus 1 tablespoon (156g) sifted cake flour
1 cup (200g) granulated sugar
3/4 teaspoon (4g) baking powder
1/4 teaspoon (1.5g) baking soda
1/2 teaspoon (3.5g) salt
14 tablespoons (200g) unsalted butter, softened

Preheat oven to 350F and line a a 9-inch springform pan with a 9-inch round of parchment paper on the bottom, then spray the parchment paper and sides of the pan with a flour/oil baking spray (hold the parchment paper in place with a dab of butter or shortening).  In a small bowl, whisk together the cocoa, sour cream, eggs, and vanilla.  In the bowl of a stand mixer, combine the remaining dry ingredients.  Add the butter and cocoa mixture; mix on low for 30 seconds, then increase the speed to medium and continue mixing for about 2 minutes.  Spread the batter into a smooth layer in the prepared pan.  Bake for 30-40 minutes or until a toothpick comes out of the center of the cake clean (one or two crumbs are okay).  Cool cake completely.

To decorate like shown:
Lay a template in the center of the completely cool cake.  Sprinkle an even layer of powdered sugar over the entire surface of the cake and carefully removed the template.  Pipe a buttercream border around the edges and sprinkle with shaved chocolate. 

Chocolate Egg White Buttercream
makes about 2 cups (double to frost an entire 9-inch cake)
adapted from The Cake Bible

5 ounces (142g) bittersweet chocolate
1 cup (227g) unsalted butter, softenend
2 large (60g) egg whites
1/2 cup (100g) granulated sugar

Gently melt chocolate in microwave on high, stirring every 10-15 seconds until almost completely melted.  Rely on the residual heat to finish melting the chocolate as you continue to stir; set aside to cool.  In the bowl of a stand mixer, whip the egg whites until soft peaks form; slowly add sugar and continue beating until stiff peaks form.  Gradually add the room temperature butter, a tablespoon at a time, until it's fully incorporated.  Add the cooled melted chocolate and whip until fully combined.  Note:  use pasteurized egg whites if you have any concerns about using fresh egg whites.