Mix flour, icing sugar, vanilla sugar & salt.
Add the butter & the egg & knead everything together.
Form a ball & let it chill in the fridge for about 30 min.
Clean & trim the plums. Cut them into halves & discard the pits.
Preheat the oven to 180° C fan.
Roll out the pastry between 2 sheets of clingfoil & transfer the pastry (w/o the clingfoil!) to the tart form. Fit the pastry into the tart form.
Bake in the preheated oven for about 15 min.
Reduce the oven temperature to 160° C fan.
Whisk eggs & sugar & ricotta w/ an egg whisk until creamy.
Pour the ricotta mess in the hot pastry shell.
Add the plums on top.
Bake in the preheated oven for about 40 min.
Sprinkle some sugar all over the tart.
Let the tart cool down in the tart form & serve in it.