Grease the tart pan. Knead 250 g flour with 75 g sugar, vanilla sugar, salt, butter in pieces, 1 egg yolk and 1-2 tablespoon cold water first with a hand mixer and then with your hands until smooth. Roll out on a little flour. Line the shape with it, pressing into the grooves on the edge. Prick the pastry base several times with a fork. Chill for about 30 minutes.
Wash lemons and rub dry. Finely rub the peel of 1 lemon, squeeze the lemon. Beat the eggs with 150 g sugar until frothy. Stir in the ricotta in portions. Finally stir in the lemon zest and lemon juice. Spread the mixture on the dough.
Bake in the preheated oven (electric stove 175 degrees / convection 150 degrees) on the lowest rack for approx. 40 minutes. Turn up the oven (electric stove 200 degrees / convection 175 degrees) and continue baking for 15-25 minutes. Cool in the mold.
Cut the rest of the lemon into very thin slices. Put the liqueur, 3 tablespoon water and 50 g sugar in a saucepan and cook over high heat for about 2 minutes. Add lemon wedges and simmer in the syrup over medium heat for about 8 minutes. Then let it cool down. Spread the lemon wedges on the tart. You can drizzle some of the syrup over it if you like. Let cool down.
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