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 ½ cups All-purpose flour, 2 teaspoon Baking powder, 1 teaspoon Baking soda, 1 teaspoon Salt
Using a mixer, beat the butter, oil, and sugar on high speed for 3 minutes. It will become pale in color. Add the sour cream and vanilla and mix until combined.
¾ cup Unsalted butter, ¼ cup Oil, 1 ½ cups White granulated sugar, ½ cup Sour cream, 2 teaspoon Clear vanilla extract
Add the egg and egg whites one at a time and mix on medium speed until combined.
1 Large egg, 4 Egg whites
Add ⅓rd of the dry ingredients and half of the buttermilk and mix on low speed. Add another ⅓rd of the dry ingredients and the rest of the buttermilk. Then, finish with the rest of the dry ingredients.
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.