Preheat oven to 325° F. Line two 8 or 9" round cake pans with parchment paper and then spray with nonstick cooking spray. Set aside.
In a large bowl, combine flour, baking powder, baking soda, and salt. Set aside.
In a liquid measuring cup, combine milk and vanilla extract. Set aside.
In a stand mixer, stir butter, oil, and sugar together until combined. Add-in, one at a time the eggs and egg whites, until the mixture is light and fluffy. Scrape the sides of the bowl and mix again.
Alternate adding in the flour mixture and the milk mixture, starting and ending with flour. Scrape the sides and mix again to ensure a lump-free batter.
Divide the batter evenly between baking pans and smooth the tops.
Bake for 30-40 minutes in the lower two thirds of the oven.
Cool 15-20 minutes in the cake pans then flip the cakes onto cooling racks. Cool completely before frosting and decorating.