In a mixing bowl, combine flour, sugar, vanilla sugar, and salt.

Add egg and mix until the dough forms.

Knead lightly, wrap in plastic, and chill for 15 minutes.

Preheat oven to 230°C (446°F).

Roll out the dough and press it into a tart pan.

Prick the bottom with a fork.

Bake for 15 minutes until lightly golden.

In a bowl, whisk eggs, egg yolks, sugar, and salt until smooth.

Add heavy cream, fresh lemon juice, and zest, whisking until combined.

Lower oven temperature to 150°C (300°F).

Pour the lemon cream mixture into the pre-baked tart shell.

Bake for 17-20 minutes until the filling is set but slightly wobbly in the center.

Let cool before slicing.

Dust with powdered sugar or decorate with whipped cream and lemon zest.