For the hazelnut muffins, beat the eggs with a mixer until frothy. Add sugar, vanilla sugar and nisslikör or rum and beat for 2 minutes until foamy, add lukewarm water and continue to stir, gradually add the oil.
Mix flour with baking powder, cocoa and hazelnuts and fold in at the end. Fill muffin cups halfway with batter and bake in preheated oven for about 15-20 minutes.