For the cake, grease a springform pan with a high rim (26 cm Ø; approx. 8 cm high). Mix flour, 60 g sugar and 1 pinch of salt in a bowl. Add 1 egg and 125 g butter in pieces. First knead everything with the dough hooks of the mixer, then briefly with your hands until smooth. Cover and chill for about 30 minutes.
Roll out the dough onto some flour and make it round (about 32 cm Ø). Line a baking tin with the dough and press down well at the edges.
Melt 50 g butter over low heat. Separate 5 eggs. Beat 5 egg yolks and 200 g sugar until creamy. Stir in mascarpone and quark briefly one after the other. Stir in liquid butter, lemon peel and lemon juice.
Stir in the starch. Beat 5 egg whites and 1 pinch of salt until stiff, while adding 100 g sugar. Fold into the quark mixture and spread into the mould.
Bake in the preheated oven (electric oven: 175 °C/circulating air: 150 °C/gas: see manufacturer) for approx. 35 minutes. Take out of the oven, cut a 2 cm deep cut all around between the edge of the dough and the cheese mixture. Let it rest for 10 minutes and bake at the same temperature for 20-25 minutes. Let it cool down in the springform pan for at least 4 hours.
For the blackberry sauce, select and wash the berries. Heat jelly and remove from heat. Mix in the berries. Spread on the cake, leaving about 2 cm of edge free. Dust with icing sugar.