Mix flour, baking powder and sugar in a mixing bowl. Add egg and cold butter in pieces. First knead with the dough hooks of the hand mixer, then continue kneading with your hands to a smooth short pastry.
Cover the dough and put it in a cool place for about 30 minutes. Roll out the shortcrust pastry on a floured work surface to form a circle (approx. 30 cm Ø). Line a greased springform pan (26 cm Ø) sprinkled with breadcrumbs so that the pastry is approx. 2 cm high at the edges.
Press the dough well and prick the base of the dough several times with a fork. Refrigerate the mould again. For the nut mixture, melt butter and sugar in a pot while stirring. Stir in hazelnuts and milk.
Remove from the heat and let it cool down for about 10 minutes. Pour the mixture evenly onto the shortcrust pastry base. Bake in the preheated oven, 2nd shelf from below, (electric oven: 200 °C/ gas: level 3) for approx. 25 minutes.
In the last approx. 5 minutes cover up if necessary. Let the cake cool down. Carefully remove the dough from the rim and remove the edge of the springform pan. Turn the cake onto a grid and remove the bottom of the springform pan. Coarsely chop the chocolate coating and melt it on a hot water bath.
Cover the cake with chocolate coating and let it dry. Lift the finished cake onto a cake plate and cut it into approx. 20 pieces. Turn over every second piece. Decorate the upside-down pieces without chocolate coating with cream tuffs and hazelnut kernels as desired.