Beat egg whites with water until stiff, sprinkling in sugar and vanilla sugar. Simply knock in the egg yolks for a short time.
Sieve the flour and baking powder on top and fold in carefully and thoroughly with the whisk.
Spread the mixture smoothly in the springform pan (26cm), which is only greased on the bottom, and bake in a preheated oven at 175 ° C (fan oven) for about 30 minutes. Remove from the edge of the mold with the knife, allow to cool and divide horizontally.