Preheat oven to 350°F / 175°C. Line four 7" or three 8" pans with parchment rounds, and grease with non-stick baking spray.
Mix together 3 cups all purpose flour, 3 cups sugar, 2 1/2 tsp baking powder and 1 tsp salt in a stand mixer with a paddle attachment or hand mixer until fully combined.
Mix in 1 cup of room temperature, unsalted butter slowly into the dry ingredients on a low speed. Continue to mix until no large chunks of butter remain and the mixture looks like moist sand.
Pour in 1 cup of egg whites and mix on low until just incorporated. Mix in 1 1/2 cups buttermilk in two installments, on a low speed.
Add in 2 Tbsp of vegetable oil and 2 tsp of vanilla extract and mix at a low speed until fully incorporated.
If you plan to color your cake layers, add in the gel food coloring with the vanilla and oil.
Scrape down the sides of the bowl with a rubber spatula, then beat on a medium speed for about 30 seconds to make sure everything is properly mixed together.
Divide the batter evenly between your prepared pans. I like to use a scale to make sure each pan has the same amount of batter and will bake up to be the same height.
Bake for 33-35 minutes or until a toothpick comes out with a few moist crumbs.
Allow the pans to cool for 10 minutes, then run a small offset spatula around the perimeter of the pan to separate the cake from the pan.