Preheat the oven to 340 °F. To make the cake, add all cake ingredients except the last 2 in a stand mixer bowl and on medium speed, mix until smooth. If you do not have a stand mixer, use a hand mixer or mix by hand. Add the sour cream and egg whites and mix until smooth, about 2 minutes.
Size and shape of the pans determine baking time. You can do 3-8" or 4-6" round pans. You can also do cupcakes as well and decorate each individually. Grease your pans with butter on the bottoms, sides, and creases of pan and then dust with flour to cover the bottoms, sides, and creases. You can also use non-stick spray, but that doesn't always ensure your cakes won't stick. Pour batter into your pans, as best you can, into even amounts, no more than half full as the cakes will rise when baking. To prevent cakes from being rounded at the top, I use Wilton cake strips, and they are a game-changer in getting level cakes.
Start checking the cakes at 30 minutes then every 5 minutes after. The cakes are done when they are set and a toothpick in the center comes out clean. Once out of the oven, let the cakes cool. Once cool, turn the cakes upside down onto wax paper, cover with wax paper, wrap with foil, and freeze. Make sure the cakes are stacked evenly in the freezer and the foil or any other objects aren't denting the cakes. Freezing the cake layers will allow for easier decorating and frosting later.