1½tsplemon juice (½ tsp per egg white)substitutes: ½ tsp cream of tartar
whipped cream frostingsee Tips for recipe link
Instructions
Baking the Cake
Carefully separate the egg white from the egg yolk into separate mixing bowls. It's important that there are no egg yolks in the egg white! We do this step first so that the eggs can come up to room temperature while we prepare the subsequent steps.
If using a mixer, put the whisk or beater and the mixing bowl into the freezer. The cold equipment will enable the the egg whites to change into meringue much faster.
Trace the bottom of a 9 inch round baking pan on parchment paper and cut it out. Make sure the cut-out can fit in the round baking pan and trim, if necessary. (Optional: Repeat once more for the second baking pan, if you want to have two different color layers of cake). We will line the bottom of the baking pans with these cut outs later.
Scoop ⅓ C of flour into a 9 inch round baking pan. From the baking pan, scoop out 1 tbsp of flour (unneeded). Add 1 tbsp of cornstarch and ¼ tsp baking powder to this mixture. With a fine sieve, sift the contents of this baking pan into the other baking pan. Sift back and forth 3-4 times. (Note: replacing the flour with the cornstarch is an easy way to substitute for cake flour!)
Preheat the oven to 350°F
Mix ¼ C sugar with the egg yolks and beat on high for about 1 minute until the batter turns pale yellow. Sift the flour/baking powder mixture into this batter and beat on low until there are no dry batter. Stir in the vanilla, oil, and milk and mix until the batter is smooth. (Optional: If you want to have two different color layers of cake, separate this batter into 2 different mixing bowls and mix in your desired food coloring to each batter)
Grease bottom of the 9 inch round baking pan(s). Line the bottoms with the parchment paper cut out. Do not grease the sides of the baking pan. This will allow the batter to stick to the side and climb higher to achieve a lighter cake!
Remove the whisk/beaters and mixer bowl from the freezer. Add the egg whites to the mixer bowl and beat until it becomes foamy. Add the 1½ tsp lemon juice to the egg whites and continue beating on high until stiff peaks form (about 3 minutes). You have "stiff peaks" if you're able to turn the bowl upside down and nothing moves. Decrease the speed of the beating to low and gradually add in the remaining ¼ C sugar. Increase the speed to high again and beat until all the sugar is mixed in (about 30 seconds). And you've made meringue!
Add the meringue to the egg yolk batter. (Optional: If creating 2 different color layers, split the meringue between the two egg yolk batters). Use a spatula to gently fold the meringue in with as few strokes as possible. To have the fluffiest cake possible, don't overmix!
Pour this batter into the baking pan(s). Drop the baking pans from a height of about 6 inch onto the countertop 2-3 times to get out any air bubbles. Bake for about 15-20 minutes or until the tops of the cakes are golden brown.
Upon removing the cake(s) from the oven, let cool for about 10 minutes. The cake will seemingly deflate as it cools. Turn the pans upside down on a cooling rack so that the the cake can cool down completely.
Fashion the cake into a Butterfly
(Optional) If you created two color layers, frost the top of one layer. Then stack the second layer on top of the first.
Cut the circular cake in half and place the rounded edge against each other to form the wings of the butterfly.
Cut out a little triangle on each straight edge about ⅓ from the bottom to give detail to the wings of the butterfly.
Frost the top and sides of the cake. Draw butterfly antennas and decorate.