Sponge cake with Banana

Ingredients: Almond Sponge: 5 egg whites 120 g sugar a pinch of salt 5 egg yolks 90 g plain flour 10 g cornflour 20 g cocoa powder 50 g ground almond 2-3 large...

As I know sponge cake recipe used to start with beating egg and sugar till light and fluffy before adding any dry ingredients. I tried before and end up failure. I did beat the egg mixture till light and fluffy. It turns into disaster once I add in flour.