For the sponge dough, preheat the oven to 200 °C. Separate the eggs. Whisk yolks with water and sugar until foamy. Mix flour, nutmeg, cornflour and baking powder and stir in.
Beat egg whites until stiff and fold in carefully. Line baking tray with baking paper and spread dough evenly on it and bake for 10-15 minutes.
Immediately turn out the dough, preferably onto a kitchen towel and roll up loosely before it has cooled.