MAKE SPONGE CAKE LAYERS: Into a large bowl, separate 5 eggs and add the egg yolks to the bowl. (refrigerate egg whites for other baking). Add 8 full eggs and 1 cup sugar. Using mixer, beat on high speed for 8-10 minutes until eggs are light in color, thick and fluffy. Sift 1 cup all-purpose flour into the fluffy egg mixture one third at a time. Fold with a hand whisk (works the best) with each addition just until incorporated. Scrape from the bottom making sure no streaks of flour remain. (Do not over-mix or you will deflate the batter).