Cream fat, 150 g sugar, vanillin sugar and salt with the whisk of the hand mixer. Add the eggs bit by bit. Mix flour, cornstarch and baking powder and stir in portions. Pour the dough into a greased springform pan (26 cm Ø) sprinkled with flour and bake in a preheated oven (electric range: 175 °C/ gas: level 2) for approx. 25 minutes. Let it cool down. Mix grapefruit juice, quark and 100 g sugar to a smooth mixture.
Soak gelatine in cold water for approx. 5 minutes. Whip cream until stiff. Squeeze out the gelatine, warm it up while stirring until it is completely dissolved. Mix 2-3 tablespoons of the quark mixture with the gelatine. Add the gelatine quark mixture to the remaining quark mixture, stir, fold in the cream. Pour the quark and cream mixture onto the cake base, smooth it down and put it in a cool place for about 4 hours. In the meantime, peel the grapefruit so that the white skin is completely removed. Cut the grapefruits into thin slices, dab dry a little and cover the cake with them. Mix the cake glaze powder with the remaining sugar in a saucepan, adding 250 ml of water little by little. Bring to the boil while stirring. Spread the glaze evenly from the middle of the cake.
Pour the quark and cream mixture onto the cake base, smooth it down and put it in a cool place for about 4 hours. In the meantime, peel the grapefruit so that the white skin is completely removed. Cut the grapefruits into thin slices, dab dry a little and cover the cake with them. Mix the cake glaze powder with the remaining sugar in a saucepan, adding 250 ml of water little by little. Bring to the boil while stirring. Spread the glaze evenly from the middle of the cake. Let it cool down. Results in about 12 pieces
waiting time approx. 4 hours