Knead the flour, 100 g sugar, 1 egg, 200 g butter in pieces and 1 pinch of salt first with the dough hooks of the mixer, then briefly with your hands to a smooth shortcrust pastry. Wrap in foil and chill for about 30 minutes.
Grease a fat pan of the oven (deep baking tray; 32 x 39 cm). Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2). For the poppy seed mixture, drain the apricots well and dice finely.
Mix poppy seed filling, 250 g sour cream, 4 eggs and 1 pudding powder until smooth. Fold in diced apricots. For the quark mixture, mix quark, 250 g sour cream, 5 eggs, 250 g sugar, 1 pudding powder, vanilla sugar and lemon juice.
Roll out the dough on the bottom of the fat pan and prick several times with a fork. First spread the poppy seed mixture evenly on top, then spread the quark mixture on top. Bake in the hot oven on the lower shelf for 50-60 minutes.
Let it cool down. Then whip cream until stiff. Cut the cake into about 24 pieces, decorate with cream tuffs and possibly with unground poppy seeds.