Wash the lemons hot, dry them off, rub the peel thinly. Halve the lemons and squeeze them.
Preheat oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer). Grease a box form (25 cm long; approx. 1.7 l capacity) and dust with flour. Whisk 180 g butter, 180 g sugar, 1 vanilla sugar, 1 pinch of salt and lemon zest until light creamy. Stir in the eggs one by one. Mix 200 g flour and baking powder and alternately stir in approx. 75 ml lemon juice briefly. Fill the dough into the form, smooth it down. Bake in a hot oven for 45-55 minutes (stick test). Cover the cake with aluminium foil after about half the baking time. Take out and let cool down for about 20 minutes. Turn the cake out of the tin and let it cool down.
Whip the quark, mascarpone, 1 tbsp. sugar and 1 vanilla sugar with the whisks of the mixer until thick and creamy. Spread loosely on the cake, chill for approx. 30 minutes.
Select the berries and wash them carefully, drain them. Before eating, spread the berries on the cream.