Preheat oven to 350°F. You can line your pans with parchment on the bottom and sides if you wish for easy removal, use a cake release spray or the cake release recipe.
Add all dry ingredients (flour, cocoa powder, baking powder, sugar, and salt) to a stand mixer bowl and mix with a paddle to combine well. This replaces sifting. (pictures do not include the cocoa powder, just to be used as reference to mixing method)
In a separate bowl, combine all wet ingredients (vanilla bean paste, egg whites, milk, and vegetable oil) and whisk to combine. Set aside.
Turn mixer to low and add room temp chunks of butter slowly to the dry mix.
Continue to beat on slow until there are no chunks of butter remaining and the mixture becomes crumbly. Your dry ingredients and butter mixture should crumble when squeezed gently, hold it’s shape.
On low speed, add 1/3 of the liquid ingredients to the dry/butter ingredients and then turn to medium. Mix until a light paste forms. Scrape down the sides of the bowl.
Add half of the remaining wet ingredients and beat on medium high speed for 4 minutes. Scrape down the sides and bottom of the bowl.
Add the remaining wet ingredients and beat on medium speed for 5 minutes.
Fill desired pans 2/3 of the way full.
Bake until a skewer comes out clean and sides have begun to pull away from the side of the pan. (see additional notes below)
Allow to cool for 10 minutes before removing from pan. Place on a rack to finish cooling.