Preheat the oven to 350℉. Spray a 8X8 inch cake pan with baking spray. Line the bottom with parchment paper circle and spray again. Set aside.
In a medium bowl, sift the flour, baking powder, baking soda, and salt. Set aside.
1 3/4 cups Cake flour, 1 tsp Baking powder, 1/4 tsp Baking soda, 1/2 tsp Salt
Using a mixer in a large bowl, beat the butter, oil, and sugar on high speed for 2 minutes.
1/2 cup Unsalted butter, 1 cup White granulated sugar, 2 TBSP Oil
Add the vanilla, sour cream, and egg whites. Mix on medium until combined. Add the dry ingredients and buttermilk. Mix on low speed until combined. Take off the mixer and scrape the bowl.
1 TBSP Pure vanilla extract, 1/4 cup Sour cream, 1/2 cup Buttermilk, 3 Large egg whites
Spread the cake batter into the cake pan. Bake for 34-39 minutes. Bake until a toothpick inserted comes out clean.
Let the cake sit in the hot pan for 10 minutes before transferring to a cooling rack. Cool the cake completely before decorating.