Preheat Oven to 350˚F. Line bottoms of two 9″ cake pans with parchment paper (do not grease the sides).
How to Make this Sponge Cake:
In the bowl of an electric stand mixer fitted with whisk attachment (this is the one I have), beat 6 large eggs for 1 minute on high speed. With the mixer on, gradually add 1 cup sugar and continue beating 8-10 minutes until thick and fluffy.
Whisk together 1 cup flour and 1/2 tsp baking powder then sift this mixture into fluffy egg mixture one third at a time. Fold with a spatula with each addition just until incorporated. Scrape spatula from the bottom to catch any pockets of flour and stop mixing when no streaks of flour remain. Do not over-mix or you will deflate the batter.
Divide evenly between prepared cake pans (it helps if you have a kitchen scale to weight the pans). Bake at 350˚F for 23-28 minutes (my oven took 25 min), or until top is golden brown. Remove from pan by sliding a thin spatula (here’s the one I love for cakes) around the edges then transfer to a wire rack and remove parchment backing. Cool cakes to room temperature then slice layers equally in half with a serrated knife.