Combine dry ingredients (flour, baking powder, sugar, and salt) in a mixing bowl *if using a stand mixer, use a paddle attachment not a whisk.
In a separate bowl or large glass measuring cup, whisk vanilla, egg whites, milk, and vegetable oil.
With the mixer on low, add chunks of butter slowly to the dry mix.
Mix until no lumps remain, the mixture will become crumbly
Add 1/3 of the liquid ingredients to the dry ingredients (it will look like a thick brownie batter) scrape down the bowl.
And in another 1/3 or the wet and beat on medium high for 4-5 mins
Scrape the bowl down and add the final 1/3 of the wet ingredients and mix on medium speed for an additional 5 mins.
Pour into prepared cake pan.
Bake for 50 minutes, or until a skewer comes out clean and sides have begun to pull away from the side of the pan.
Allow the cake to cool completely inside the pan. Decorate with buttercream or cream-cheese frosting.
Notes
Add Vanilla Paste: To up the flavor try using fresh vanilla bean or vanilla paste.
More Moisture: Replace the oil with sour cream, yogurt or even mayonnaise.
Do Not Over Beat: Beat until just everything is combined for a feathery light cake.
Line: Take the time to line your cake pans. You can buy pre cut ones or here is a video that will show you how to cut them.
Oven thermometer: Use an oven thermometer to ensure that you are baking at the right temperature, they are inexpensive and can save a cake from being too done.
Dietary consideration tip: Use a gluten free cake flour. Like this one.