Wash the grapes, pluck the stems and pour the white wine over them in a small saucepan so that they are covered. Bring to the boil and let cool in the wine. In the meantime, stir the butter with the sugar until foamy, stir in the egg and knead with the flour and hazelnuts. Do not let the dough rest! Grease a springform pan (26 cm diameter), spread 2/3 of the dough on the springform pan base, form a small edge. Spread the cooled, well drained grapes close together, knead the crumble from the remaining dough and spread over the grapes. Bake in a preheated oven at 200 degrees for about 30 minutes. Serve with whipped cream with vanilla sugar. Can you eat lukewarm or cold!