Rinse lemons hot, rub dry. Finely grate the zest, halve the lemons and squeeze the juice. Cream butter, sugar, vanillin sugar and 1 pinch of salt with the whisk of the hand mixer for about 5 minutes.
Add lemon peel and juice. Stir in eggs, sour cream and 3 tbsp. curd. Carefully stir in flour and baking powder.
Grease a springform pan (26 cm Ø), pour in the dough, smooth it down and bake in the preheated oven in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 25 minutes.
In the meantime warm up the remaining lemon curd (do not boil). Mix powdered sugar, milk and curd and put aside. Take the cake out of the oven and let it cool down for about 1 hour. Remove cream puffs from the freezer about 45 minutes before serving and allow to defrost.
Spread cream puffs over the cake and sprinkle with the icing.