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 — 350º F/177º C. I tend to use lower setting to prevent my cakes from getting too dark on the outside before the inside is done baking.
Prepare two three 6"x2" cake pans with cake goop or another preferred pan spray. Fill your pans about 3/4 of the way full of batter.
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.
Combine 1/2 cup of the milk and the oil together and set aside.
Combine the remaining milk, egg whites, pink food coloring and vanilla together, whisk to break up the eggs and set aside.
Add your softened butter to the dry ingredients and mix on low until mixture resembles a 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 minutes to develop the cakes 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 mixture in three batches, letting the batter mix for 15 seconds between additions.
Scrape down the sides again to make sure everything has incorporated then pour into prepared pans. Bake 35-40 minutes until a toothpick inserted into the center comes out cleanly but the cake has not begun to shrink yet from the sides of the pan. 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. Flip onto a cooling rack and let cool fully. I chill my cakes before handling or you can wrap them in plastic wrap and freeze them to trap moisture in the cake. Thaw on the countertop while still wrapped before frosting.