• Preheat oven to 350°F. Grease and flour 2-9 inch cake pans. 
• In a medium bowl whisk the cake flour, baking soda, coca powder, and salt. 
• In a medium bowl mix the egg whites until stiff peaks form (be careful not to overbeat the whites). 
• In the bowl of a stand mixer fitted with the paddle attachment cream the butter and sugar on medium speed for 2-3 minutes. Scrape down the sides of the bowl as needed. Add the oil, egg yolks, vanilla, and vinegar. Mix until combined. 
• Alternate adding the dry ingredients with the buttermilk, starting and ending with the dry ingredients. Scrape down the sides of the bowl as needed. Add 2 (or more) teaspoons of gel red food coloring. Mix to combine.
•  Using a rubber spatula, fold the egg whites into the cake batter.
• Divide the batter amongst the 2 cake pans. Tip: use a kitchen scale to ensure even amounts of batter are in each pan. 
• Bake for 29-33 minutes or until a toothpick inserted in the center comes out with a few moist crumbs, but no wet batter. See note #1. (The tops of the cake should lightly spring back when touched). Remove from the oven and let cool in the pans for 10 minutes then turn out on a cooling rack to cool before frosting. 

Frosting

• To make super fine sugar, place the granulated sugar in a food processor. Process for 2 minutes. Ta-da! Super fine sugar. 
• In a small saucepan whisk the flour and milk over medium heat until thickened (be sure to whisk constantly to prevent clumping). The mixture should come to a simmer, at this point you'll notice the mixture thickening. Once thick, remove from heat to let cool slightly. Place plastic wrap directly on the flour/milk mixture and place in the refrigerator to chill, about 2 hours.
• Once it's fully chilled continue... In the bowl of a stand mixer beat the butter, sugar, and vanilla on medium speed for 2 minutes. Add the flour and milk mixture, a little at a time. Beat on medium speed for 4-5 minutes or until no longer grainy. Add milk or heavy cream a tablespoon at a time until it reaches your desired consistency. I added 1-2 tablespoons of heavy cream.
• Frost the cooled cake. Place a cake on a cake stand or serving platter, top side up. Spread about 1/3 of the frosting over the top of the cake. Place the other cake layer over the frosting, bottom side up. Frost the top of the cake with 1/2 of the remaining frosting. Use the last of the frosting to frost the edges of the cake.