Beat the egg whites until stiff. Beat the egg yolks with the sweetener and vanilla sugar until frothy. Stir in nuts and baking powder. If the mixture is very dry, add a little milk. If the dough seems too thin, add a few more nuts. Finally fold in the egg whites.
Put the dough in a greased pan (I used a silicone Gugelhupf pan) and bake at 150 ° (fan-assisted) for 30-40 minutes. When the cake is done, it will turn light brown on top.