Beat the eggs with the whisk of the hand mixer for approx. 8 minutes until creamy. Gradually add sugar and vanillin sugar. Mix hazelnuts, flour, cocoa and baking powder. Stir the flour mixture into the egg mixture and continue stirring for approx. 5 minutes. Finally stir in oil and mineral water
Pour the dough into a greased box form (10 x 27.5 cm) sprinkled with breadcrumbs and bake in a preheated oven (electric range: 150 °C/ convection oven: 125 °C/ gas: stage 1) for 1 1/4-1 1/2 hours (stick test). Remove the cake, let it cool down for about 20 minutes and then turn it out of the tin. Let the cake cool down on a cake rack
Coarsely chop the chocolate and coconut fat and melt in a bowl over a warm water bath. Remove the chocolate from the bain-marie and let it cool down a little. Roast the hazelnut leaves in a pan without fat, take them out and let them cool down
Spread the chocolate on the cooled down cake and refrigerate for about 45 minutes. Sprinkle hazelnut flakes onto the cake after about 10 minutes
waiting time approx. 2 hours