Mix flour, baking powder, sugar, vanilla sugar and salt in a big bowl. Then add the margarine. Work everything until you have a soft dough. You need to be able to form a ball. Maybe a ball that crumbles very easily, but a ball nonetheless. If it doesn't hold together, you can add a little bit of cold water - a teaspoon at a time. Roll out the dough or straight away place it in the baking pan and push it so it covers the entire bottom of the pan and goes up the edges. Aim for sides about 3 cm high.
Prick the dough with a forck a few times.
Then place the crust in the oven and bake for 15 min.
Once the crust is done, take it out of the oven, letting it cool down slightly while you prepare the filling.