Preheat the oven to 350°F. Spray three 8-inch cake pan with baking nonstick spray. Line the bottoms with 8-inch parchment paper circles and spray again.
In a medium bowl, sift the flour. Add the baking powder, baking soda, and salt. Set aside.
3 1/2 cups Cake flour, 2 tsp Baking powder, 1 tsp Baking soda, 1 tsp Salt
Using a mixer, beat the butter, oil, and sugar on high speed for 2 minutes. It will become pale in color.
3/4 cup Unsalted butter, 1/4 cup Oil, 1 1/2 cups White granulated sugar
Add in the sour cream, vanilla, and egg whites. Mix on medium speed until combined.
3/4 cup Sour cream, 5 Egg whites, 1 TBSP Pure vanilla extract
Add in the dry ingredients and buttermilk. Mix on low speed until just combined.
1 cup Buttermilk
Take the bowl off the mixer and use a rubber spatula to scrape the bowl. Pour the cake batter evenly throughout the three cake pans.
Bake for 22-25 minutes until a toothpick inserted comes out clean.
Let the cake sit in the hot pans for 10 minutes. Transfer to a cooling rack and cool completely.