Preheat your oven to 180 ° C (top / bottom heat). Make a kneading dough out of the flour, the butter, 20 g sugar and the water and cool it for about 30 minutes.
In the meantime, peel and core the apples and cut them into thin wedges. Now grease a tart pan, roll out the dough with a rolling pin on a floured work surface about 0.5 cm thick and put it in the cake pan. Pierce it several times with a fork (this will prevent bubbles from forming).
Now, starting from the outside, place the apple wedges on the dough in a rosette shape and place the tart in the oven for 25 - 30 minutes.
During the baking time, beat the eggs with the sugar until frothy and then fold in the crème fraîche. Now put the egg cream on the pre-baked tart (the apples should be soft) and bake for another 20 minutes. The sour cream should take on a golden color.