For the chocolate cupcake, melt the chocolate on the induction stove at level 2 (otherwise in a bain-marie). Beat the eggs with the sugar until it has dissolved.
Add the vanilla sugar and stir in the chocolate. Beat in the oil very slowly, add the salt and stir in the hazelnuts.
Sift the flour with the baking powder and cocoa and slowly stir into the egg mixture and mix with the mineral water. Pour the dough into a buttered and floured loaf pan and bake at 180 °C on the middle shelf in a preheated oven for about 1 hour.
Be sure to test the needles. When cooled, decorate with powdered sugar.