Cream fat and 100 g sugar. Stir in the eggs one after the other. Add milk and lemon zest. Mix flour, cornstarch and baking powder and finally stir in briefly. Put the dough into a greased springform pan (26 cm Ø) and smooth it down. Bake in the preheated oven (electric: 200 °C/ gas: level 3) for 15-20 minutes.
Let the base cool down in the mould, then leave it in the mould. Soak gelatine in cold water. Mix mascarpone, yoghurt, 45 g sugar and vanilla sugar. Squeeze out the gelatine, dissolve it, mix with a little cream, then stir into the remaining cream. Whip cream until stiff, fold into the cream and spread loosely on the cake. Put in a cool place for about 4 hours. Wash the grapes, dab dry and, except for a few for decoration, pluck from the stems. Halve the grapes and remove the seeds. Put the cake glaze and remaining sugar in a pot. Sprinkle with grape juice and white wine. Bring to the boil while stirring and let stand for 2-3 minutes. Fold in grapes and spread on the cream.
Halve the grapes and remove the seeds. Put the cake glaze and remaining sugar in a pot. Sprinkle with grape juice and white wine. Bring to the boil while stirring and let stand for 2-3 minutes. Fold in grapes and spread on the cream. Refrigerate for another 30 minutes. Roll remaining grapes first in lemon juice, then in sugar. Remove the cake from the mould and serve decorated with grapes and mint