NOTE: It is SUPER IMPORTANT that all the room temperature ingredients listed above are room temperature and measured by weight so that the ingredients mix and incorporate correctly. Heat oven to 335º F/168º C
Prepare six ( 8"x2") cake pans with cake goop and place a round piece of parchment paper in the bottom of the pan for easy removal of the cake
Combine 8 oz of the buttermilk and the oil together and set aside.
Combine the remaining buttermilk, egg whites, and vanilla together, whisk to break up the eggs and set aside.
Combine flour, sugar, baking powder, baking soda and salt in the bowl of a stand mixer with the paddle attachment. Mix 10 seconds to combine.
Add your softened butter to the dry ingredients and mix on low until mixture resembles coarse sand (about 30 seconds).
Add in your milk/oil mixture and let mix until dry ingredients are moistened and then bump up to med (setting 4 on my KitchenAid) and let mix for 2 full minutes to develop the cake's structure. If you don't let your cake mix on this step your cake could collapse.
Scrape your bowl and then reduce speed to low. Add in your egg white/milk mixture in three batches, letting the batter mix for 15 seconds between additions. Scrape down the sides again to make sure everything has incorporated.
Divide your batter into 6 bowls. Weigh 15 ounces of batter for each bowl.
Color each bowl with your Electric food colors. 1/2 tsp for pink for the pink layer, 1/4 tsp yellow plus 1/4 tsp orange for orange layer, 1/2 tsp yellow for yellow layer, 1/4 tsp yellow plus 1/2 tsp green for green layer, 1/2 tsp blue for blue layer, 1/4 tsp pink and 1/2 tsp purple for the purple layer.
Bake your layers for 20-24 minutes or until the edges JUST start pulling away from the cake pan. Do not under-bake or the middle of the cake will collapse.
IMMEDIATELY TAP PAN FIRMLY on countertop once to release the steam from the cake. This stops the cake from shrinking.
Let cakes cool for 10 minutes inside the pan before flipping them out. The cake will shrink a bit and that is normal. Freeze your cake layers 30-60 minutes before trimming your cakes. Frost and fill with buttercream frosting.
After your buttercream is smooth, place the cake back into the fridge for 15 minutes before you apply your drip.
Wait for your drip to set before painting with gold paint. Finish the cake with buttercream rosettes and more sprinkles.