
This magic cake is very unique. It only requires 4 ingredients to make the batter. When the cake bakes, it separates into three different layers. It is a delicious and fun cake to serve to family and friends.
Preheat oven to 325°F (163°C). Line an 8 x 8 inch baking pan with parchment paper.
In a larger mixing bowl, add egg yolks, flour, sugar and 1/2 cup (4 oz) of milk. (Make sure to only add 1/2 cup right now. If you add all of the milk you will not be able to mix your batter.) Beat on high speed until batter is smooth and no flour lumps remain. Once batter is smooth, add in remaining milk (1 1/2 cups). Reduce speed on mixer and mix until milk is incorporated into the batter. Your batter will be very thin.
In a separate clean mixing bowl, add egg whites. Beat egg whites on highest speed until stiff peaks form. Your mixing bowl and mixer must be completely clean before adding and beating the egg whites, otherwise the egg whites will not turn into stiff peaks. See notes section for more tips on beating egg whites.
Gently stir and fold in 1/3 of the egg whites into the cake batter with a spatula. Because the cake batter is so thin, you do need to swirl and fold to make sure the egg whites are fully incorporated. Make sure to fold all the way from the bottom of the bowl, otherwise the liquid batter at the bottom won't get fully mixed with the egg whites. Fold until no egg white streaks remain. Repeat with the next 1/3 and then final 1/3. For the final 1/3, you do not need to mix until no egg white streaks remain. It's fine to have some small lumps of egg whites in your batter. Your batter should look very light and airy.
Pour batter into the prepared cake pan. Bake for about 40-50 minutes, or until cake is done (mine took 45 minutes). If you are unsure if your cake is done, it is better to bake a little longer (5 minutes or so) to make sure it is done so that your cake does not deflate. When the cake is done, a cake tester should come out clean. The top should be evenly browned. Let cake cool before removing and cutting. As the cake cools it will deflate a little around the sides. That is normal.
Cake can be served the same day it is baked or the next day. See notes for the difference in texture. If serving the same day, let cake for 1-2 hours before cutting and serving. If serving the next day, store cake in fridge overnight. Before serving cake, you can dust cake with powdered sugar.