Preheat oven to 350 degrees. Line two 8-inch round baking pans with parchment paper and/or spray well with nonstick cooking spray and set aside. In a large bowl, whisk flour, cocoa powder, baking soda and salt together to combine. Set aside. In a liquid measuring cup, stir buttermilk, vanilla, vinegar and red food coloring. Set aside.
In a separate large bowl, mix oil and sugar together until combined. Mix in eggs and egg white, one at a time, until mixture becomes lighter in color, about 90 seconds.
Alternate adding in flour mixture with milk mixture, being sure to start and end with flour. Scrape the sides and mix again to ensure a smooth batter.
Divide evenly between baking pans and smooth the top. Bake 28-35 minutes in the lower 2/3rds of the oven. If you're using three cake pans instead of two, you will need to bake this cake 22-30 minutes. Cake will be done when a toothpick comes out clean or mostly clean with a few moist crumbs. Cool 15-20 minutes in cake pans before trying to invert on cooling racks. Once you can handle the warm pans with your bare hands, you can flip them out. Cool completely before frosting and decorating.
For the Cream Cheese Frosting:
In a large bowl, beat cream cheese and butter together. You want them very soft, at room temperature so they cream nicely together and create a smooth frosting. Add in the powdered sugar, vanilla and salt and very slowly start to incorporate. At first, it will seem like too much powdered sugar, but as long as your butter and cream cheese were soft, it should combine. Once the powdered sugar is incorporated, increase speed to whip for 1-2 minutes or until light and fluffy. If it still seems too stiff to use as frosting, add in 1-2 tablespoons heavy whipping cream. This makes enough to frost a two layer cake. If you've baked three layers, increase recipe by 1.5 times.
1- 9×13 thick cake (bake for 30-40 minutes)
2- 8 or 9-inch round cakes (bake for 28-35 minutes)
32 cupcakes (bake for 15-22 minutes)
If you'd like a brighter red cake, use more red food coloring. Some recipes use a full 1 oz bottle, but I'd suggest using half that amount, 0.5 oz, at most. It can leave an unpleasant aftertaste, so I like to limit it. If this doesn't bother you, go nuts with the food coloring.