First, beat the egg whites with the sugar until frothy, using an electric whisk. Then stir in the milk, followed by the dry ingredients a little at a time. Finally, add the vanilla and the liquid coconut oil. Next, divide the batter equally between four bowls.
Color each portion a different color with food coloring. You can use the blue twice, putting a few more drops of it in the bowl the second time.
Mix the colored batter in a greased springform pan as follows: add a tablespoon of each color on an alternating basis so that all four are as well-mixed as possible. Finally, you can also trail the handle of the spoon through the batter to create a marbled effect.
Bake the cake for 50 minutes at 350°F in a convection oven. After it has cooled, cut it into three horizontal layers of equal thickness.
Beat the butter until it is completely soft — this can take around 10 minutes. Then slowly mix the powdered sugar into the butter. Then bring the cream cheese to the same temperature as the butter, before folding it carefully into the butter-sugar mix.
Place the first sponge layer on a cake stand and spread a generous amount of buttercream on top. Follow the same steps for the next two sponge layers. Cover the cake with the rest of the buttercream and then refrigerate for 30 minutes.
Roll out the fondant and drape it over the cake. Press it down around the sides and then cut away the excess. Use a paintbrush and some of the white food coloring to spray the fondant with 'stars.' Then you can paint it as you like, using the zodiac signs that you see in the video, for example.