Preheat oven to 350°F. Prepare three 8 inch round pans and two 6 inch round pans with baker's floured cooking spray, or grease and line with parchment rounds.
Mix together all dry ingredients (flour, sugar, baking powder, and salt) in a stand mixer with a paddle until fully combined. Mix chunks of room-temperature butter slowly into the dry mix, on a low speed. Continue to mix until no large chunks of butter remain, and the mixture becomes crumbly.
Pour in egg whites and mix on low until just incorporated. Mix in the buttermilk, vodka, Malibu rum, and blue curacao in two installments, on a low speed. Add in lemon extract and oil, and mix at a low speed until fully incorporated. Scrape down the sides of the bowl with a spatula, then beat on medium speed for about 30 seconds.
Divide batter between 5 bowls if you want colored layers – I find a kitchen scale helpful for this part, and I had about 675g in my 3 large layers and about 450 in my smaller ones. Color the large base layer blue, the middle layer and one small layer teal, and the tops light blue. It will already be slightly blue from the liqueur, so whether to add any more color is up to you! Transfer batter into the prepared cake pans.
Bake for 35-37 minutes, (or until a toothpick comes out clean). Allow to cool for 10-15 minutes before removing cake layers from pans, and cool completely before stacking and decorating. Place cake layers into the freezer for 45 minutes, to accelerate the cooling process. (While you’re waiting…make your frosting!)
(Once the layers have fully cooled, they can be leveled and any caramelized bits can be trimmed from the sides / top of the cake using a serrated knife if desired. Be sure the layers are completely cooled or chilled before trimming. If you try to trim the layers while they’re still warm, they will crumble apart.)