Beat the eggs, sugar and vanilla sugar with a hand mixer at top speed for about 10 minutes, after which the mixture must have tripled in size.
Then lightly fold in the flour with a whisk. Pour the batter into a well-greased baking dish. Bake in a preheated oven at 180°C for about 30-40 minutes.
Makes a loose, fluffy sponge for cake layers, sponge rolls, etc.
