Heat oven to 350℉/177℃.
Spray two 8-inch round pans with baking spray. Set aside.
In a medium bowl, whisk flour, baking powder, baking soda, and salt together. Set aside.
In the bowl of an electric mixer fitted with a flat beater, beat butter and sugar until creamy, about 1-2 minutes, scraping bowl as necessary.
Beat in eggs and yolks, one at a time, beating well after each addition, scraping sides and bottom of bowl as necessary.
Beat in vanilla.
Add flour mixture alternately with buttermilk, beginning and ending with flour mixture.
Divide between prepared pans.
Bake for 25 minutes, or until cake test done.
Allow to cool in pan before turning out.