Wash the lemons thoroughly, dab dry and finely grate the peel. Squeeze the lemons (approx. 120 ml juice). Cream the fat, 400 g sugar, 1 packet of vanillin sugar, lemon zest and 1 pinch of salt with the whisks of the hand mixer. Stir in the eggs one after the other, alternating with one tablespoon of flour at a time. Mix remaining flour and baking powder, add and stir in briefly.
Grease a fat pan of the oven (approx. 32 x 39 cm) and dust with flour. Add the dough and smooth it down. Bake in the preheated oven, middle shelf (electric oven: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 25 minutes.
Mix icing sugar and 100 ml lemon juice. Remove the cake from the oven and immediately sprinkle with the icing. Leave to cool for about 3 hours.
Drain the apricots well on a sieve and put 20 nice halves aside. Use the rest of the apricots and juice for other purposes. Mix mascarpone, quark, 2 tablespoons lemon juice, 75 g sugar, 1 packet vanilla sugar and milk until creamy. Whip cream until stiff and stir into the cream.
Cut cooled lemon cake into 20 pieces of approx. 8 x 8 cm. Put a heaped tablespoon of cream on each piece and cover with 1 apricot half each. Keep cool until serving.