Divide the soft fat into large pieces and place in a mixing bowl. Whisk with the whisk of the hand mixer until foamy. Add sugar, vanillin sugar and salt and stir until a creamy mixture is formed.
Separate eggs. Stir the egg yolks into the fat-sugar mixture. Wash and dry lemons and grate the peel. Squeeze 1 lemon. Stir in quark, milk, semolina, lemon peel and juice. Beat the egg whites until stiff and add to the quark mixture.
Carefully fold in with a whisk. Put the dough into a greased springform pan (26 cm Ø) sprinkled with breadcrumbs and smooth it down. Bake in the preheated oven (electric: 200 °C/ gas: level 3) for 45 minutes.
If necessary, cover with parchment paper after 30 minutes of baking time. Let the cake cool down for about 10 minutes, remove from the tin and let it cool down. Dust with icing sugar before serving.