Mix the flour with baking powder and quickly knead together with the margarine, sugar, vanilla sugar, egg yolks and the grated lemon zest to form a kneading dough and leave to rest in the refrigerator.
Preheat the oven to 180 ° C top / bottom heat.
Peel off the currants, wash and drain.
In the meantime, beat the egg white with a pinch of salt into a very stiff egg whites and slowly pour in the sugar. Loosely fold in the prepared currants and ground hazelnuts.
Now distribute the cooled dough on a greased baking sheet and brush with the mixture. Pull over the surface with a notched spatula and bake the cake on the second rack from the bottom for about 50 minutes. Let cool and cut into pieces.