Preheat your oven to 325°F and spray two 8-inch round cake pans with cooking spray and line the bottoms with parchment paper and set aside.
In a medium bowl, sift together the flour, baking soda, baking powder, and salt. Set aside.
In a large bowl with a hand mixer or stand mixer fitted with a whisk attachment, cream together the sugar, oil, butter, and vanilla.
Add the eggs and egg yolks one at a time beating after each addition just until combined.
Using a rubber spatula, fold in the dry ingredients in 3 parts alternating with the buttermilk in 2 parts. Begin and end with the dry ingredients. Gently fold until only very small lumps remain. DO NOT use an electric mixer for this step.
Evenly divide the batter between the two prepared cake pans and bake for 30 to 35 minutes. A toothpick should come clean from the center when done.
Transfer the cake pans to a wire rack and allow the cakes to cool in the pan for 10 minutes before removing and allowing to cool completely (about 1 hour) before frosting. Once cooled, frost and assemble the cake as desired.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)