Wash the grapes, drain and pluck them from the panicles. Put flour, 1 egg, 1 packet of vanilla sugar, salt and 100 g sugar in a mixing bowl. Add the fat in pieces and ground hazelnuts and knead everything into a smooth dough. Cover the dough and refrigerate for about 20 minutes. In the meantime, mix sour cream, remaining sugar and vanilla sugar and the remaining eggs. Grease a quiche tin (28 cm Ø), roll out the dough and line the tin with it.
Prick the bottom several times with a fork and sprinkle with 2 tablespoons of hazelnut leaves. Spread the grapes on the base and pour over the sourdough. Bake in the preheated oven (electric cooker: 175 °C/ gas: level 2) for about 50 minutes. Let it cool down on a cake rack and sprinkle the remaining hazelnut leaves on top. Dust with icing sugar and decorate with lemon balm