For the banana casserole, season the banana slices with sugar, lemon juice and raspberry brandy and spread in a baking dish.
Pre-bake in the oven for about 15 minutes, then beat egg whites with sugar until stiff, fold in yolks, flour and vanilla sugar and spread this mixture on the banana slices, cover with foil.
Bake in the oven at 250 °C for about 60 minutes. Sprinkle with powdered sugar to serve.