Preheat the oven to 180°C.
Separate the yolks from egg whites and beat the egg white together with 50 g of sugar until stiff.
Separately, add the luke-warm water, 150 g sugar and vanilla to the egg yolk and steer until frothy.
Add the flour and custard powder and stir well.
Add the egg whites to the mix and mix carefully.
Fill the dough in a springform pan ø 28 cm, and then cover it with a baking paper. Use a baking tray, if you use the double amount of dough.
Bake the dough in the oven for 20 minutes, until the sponge cake base is gold brown.
Let the sponge cake base cool down a bit.