For the shortcrust 75 g butter in pieces, 150 g flour, 1 egg yolk, 1 pinch of salt, vanillin sugar and 75 g sugar, first with the dough hooks of the hand mixer, then with your hands to a smooth shortcrust pastry. Roll out to a circle (30 cm Ø) on a well floured work surface. Pour the dough into a greased, flour-spread tart mould with lift-off base (26 cm Ø), pull up the rim and press down. Prick the base several times with a fork and chill for about 45 minutes. In the meantime mix 100 g flour, 50 g sugar and 1 pinch of salt. Add 1 egg yolk, 50 g soft butter in flakes and vanilla flavouring and knead everything into crumbles using the dough hooks of the hand mixer. Chop the couverture and melt over a warm water bath.
Remove from the stove and let it cool down a little. Mix sour cream, creme fraiche, 100 g sugar and milk with the whisks of the hand mixer. Stir in eggs and custard powder. Let melted chocolate coating shrink and mix. Pour the egg mixture into the tart mould on the bottom and bake in the preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: level 2) on the bottom shelf for 15-20 minutes. As soon as the mixture begins to firm on the surface, spread with crumbles and bake for 20-25 minutes. Remove the tart from the oven, place on a cake rack and allow to cool
waiting time approx. 1 1/4 hours