Melt the butter and allow to cool while mixing the other ingredients.
Whip egg and sugar well together in a bowl.
Mix flour, cocoa, salt and vanilla sugar well together in a bowl.
Then mix in egg and sugar mass, along with the melted butter.
Everything mixes well together.
Then chop the hazelnuts roughly.
Then pour the dough into a pan with baking paper.
Then sprinkle the coarsely chopped hazelnuts beyond the cake.
The cake is baked at 180°C / 320°F for 25 minutes.
The cake must cool before it is cut.