Grease a fat pan (approx. 32 x 39 cm; approx. 3.5 cm deep) and dust with flour. Cream the fat, 200 g sugar and lemon zest with the whisks of the hand mixer. Stir in the eggs one by one. Mix flour and baking powder and stir in alternately with 100 g liquid cream in portions. Spread on the fat pan. Bake in the preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for approx. 15 minutes. Let them cool down
Whip 500 g cream until stiff, while pouring in 1-2 sachets of cream firming agent. Mix quark, 150 g sugar, vanillin sugar and 2 sachets of cream firming agent. Immediately fold in the cream. Spread on the cake base. Cut the cake crosswise into 5 approx. 7 cm wide strips and lift them from the fat pan
Brush the strips with red fruit jelly shortly before serving. Cut into approx. 5 pieces each. Beat 150 g cream until half stiff, spread on the slices and decorate with lemon slices