Melt 275 g butter. Put flour, 175 g sugar, vanillin sugar, melted butter and salt into a bowl and knead first with the dough hooks of the hand mixer, then with your hands to a crumbly dough. At the end mix in 1 tablespoon of sugar
Place about 2/3 of the crumbles in a greased tart mould (26 cm Ø) with lift-off base, sprinkled with breadcrumbs. Press the crumbles as base and edge (approx. 2 cm high) firmly. Refrigerate the tart mould and the remaining crumbles
Squeeze the lemons and take off 2 tablespoons of lemon juice. Measure the remaining lemon juice and fill up to 450 ml with water. Boil up lemon juice, 175 g sugar and 15 g butter. Mix starch and a little cold water until smooth and thicken the juice. Simmer for about 1 minute while stirring. Whisk the egg yolks, mix with 3 tbsp. lemon cream and fold into the cream. Bring the cream to the boil again briefly, then pass it through a sieve (because of the hail cords). Let the cream cool down a bit
Pour the cream into the tart and sprinkle with the remaining crumbles. Bake the tart in the preheated oven on the lower shelf (electric oven: 175 °C/ convection oven: 150 °C/ gas: level 2) for 25-35 minutes. Carefully remove the finished tart from the edge with a knife and let it cool in the tin on a cake rack
Mix icing sugar and 2 tablespoons lemon juice to a smooth glaze. Put the icing in a small piping bag and cut off a small corner. Pour the icing in strips over the cake. Let the cake cool down (otherwise it is very difficult to cut)
Waiting time approx. 1 hour