Instructions

CAKE

1. Adjust an oven rack to the middle position and heat oven to 350 degrees.  Grease two 8-inch round cake pans with 2-inch sides with non-stick baking spray. In a large bowl, add flour, 1 ½ cups sugar, baking powder, baking soda, salt and whisk to combine. In a medium bowl, whisk together buttermilk, melted butter, egg yolks (6 total), oil and vanilla.
2. Fit a stand mixer fitted with the whisk attachment and whip egg whites and cream of tartar together on medium-low speed until foamy, about 1 minute. Increase the speed to medium-high and continue to whip until whites are fluffy, about 1 to 2 minutes. Slowly add remaining 1/4 cup sugar and whip until glossy and stiff peaks form about 2 to 3 minutes. Transfer egg whites to a bowl and set aside.
3. In the now empty mixer bowl, add flour and mix on low speed, slowly pour buttermilk mixture into the flour mixture while the mixer is running. Whip batter for about 15 seconds. Scrape down bowl and continue to whip on medium-low speed until smooth and completely combined about 10 to 15 seconds.  
4. Using a rubber spatula, fold one-third of egg whites into batter, then add remaining egg whites and gently fold together until no whites remain.  Divide batter evenly between prepared cake pans and smooth tops with a rubber spatula and lightly tap pans on counter to release air bubbles.
5. Bake until toothpick inserted in the center of the cake comes out clean or with a few moist crumbs attached, about 20 to 25 minutes. Let cakes cool in pans their pans on wire racks for 10 minutes. Remove cakes from their pans and let cool at least 2 hours before frosting. 

FROSTING

1. While cakes cool prepare frosting. In a food processor, process butter, sugar, cocoa, and salt until smooth, about 30 seconds, scraping sides of bowl as needed. Add corn syrup and vanilla and process until combined about 5 to 10 seconds. Scrape down the sides of the bowl if necessary and continue to process until smooth, about 10 to 15 seconds.

ASSEMBLE

1. Place 1 cake layer on the cake platter or pedestal and place about 1 cup of frosting in the center of cake, using a large cake spatula, spread in an even layer right to the edge of the cake. Place second layer of cake on top making sure the cake layers are lined up.  Then add remaining frosting on top, and spread frosting  to the edges and onto the sides of the cake. Create billows by pressing the back of a spoon into the frosting and twirl spoon as you lift away.