1. Gather the ingredients.
2. Preheat the oven to 425 F. Line two 15-inch by 12-inch pans with parchment paper and brush the surface of the paper with butter. Set them aside for a moment.
3. Using an electric beater, beat the egg whites on high until they become foamy and start to expand. Sprinkle in the sugar, one teaspoon at a time, until all of it is incorporated into the egg whites. Continue beating the meringue until it is glossy and holds stiff peaks.
4. In a separate bowl, beat the ground almonds, confectioners' sugar, and whole eggs on medium just until the mixture becomes light and foamy.
5. Gently stir the all-purpose flour into the almond batter.
6. Then, gently stir 1/4 of the almond batter into the whipped egg whites. Fold the remainder of the almond batter and the melted, cooled butter into the egg white
7. Divide the sponge cake batter between the two prepared pans and bake the cakes for 5 minutes, until the surfaces spring back from a light touch.
8. Cover the top surface of each cake with a fresh piece of parchment and carefully invert them onto a clean surface. Slowly peel back the old parchment from the cakes and allow them to rest loosely over the cakes to prevent them from drying out.