Preheat your oven to 350*F. Grease and Place parchment rounds in 3 8'' round cake pans. I always use baking strips for my vanilla cakes. If using them, wet them and pin them on pans now.
Place Butter, oil, and sugar in your mixer and turn onto low. You want to mix just enough to incorporate it together. About 30 seconds.
Add you egg whites. Mix on low until the butter mixture has just adsorbed the egg whites.
Next sprinkle in your dry ingredients. Once they are all in, turn the mixer on low, pulsating if needed so you don't throw the flour back out. mix until it is just incorporated. About another 30 seconds.
Next add in the cup of milk. It is important that the milk is not cold. You do not want your butter to curdle back up. Once the milk is incorporated, turn the mixere up to medium and let it mix for 1 minute. scraping down the bowl midway.
Poor evenly into the prepared pans and bake for 30-35. Remove when centers are firm and toothpick comes out clean