In a large mixing bowl, combine the flour, salt, almond powder, sugar, and vanilla sugar. Mix the ingredients lightly with your fingertips to distribute them evenly.

Make a well in the center of the mixture and add the cold, diced butter. Using your fingertips, rub the butter into the dry ingredients until the mixture resembles coarse breadcrumbs or large crumbs.

Add the egg and liquid vanilla to the center. Gradually knead the mixture until it comes together into a smooth, uniform dough. Avoid overworking the dough to keep it tender.

Form the dough into a ball, wrap it in plastic wrap, and refrigerate for at least 2 hours to allow it to rest. (Alternatively, roll it out immediately, line the tart mold, and refrigerate while preparing the filling.)

Roll the dough between two sheets of baking paper to prevent sticking. Aim for an even thickness of about 3-4 mm.

Transfer the rolled-out dough to a tart mold or tart ring, pressing it gently into the edges. Trim any excess dough from the sides for a neat finish.

Prick the base of the pastry all over with a fork to prevent it from puffing up during baking. Refrigerate while you prepare the filling.

Preheat your oven to 190°C (375°F) to prepare for baking.

In a mixing bowl, beat the eggs, sugar, and vanilla sugar using an electric mixer until the mixture is pale and slightly frothy. This ensures the filling will be light and airy.

Add the almond powder and liquid cream to the mixture. Stir well until smooth and fully combined.

Take the prepared shortcrust pastry out of the refrigerator. Arrange the apple slices in concentric circles or any decorative pattern you like, pressing them down lightly to ensure they sit evenly.

Pour the filling mixture evenly over the apples, ensuring it spreads to cover all the gaps.

Place the tart in the preheated oven and bake for 30 to 40 minutes, or until the filling is set and the edges of the pastry are golden brown.

Check the tart after 30 minutes to avoid overbaking; the filling should be firm but slightly jiggly in the center.

Remove the tart from the oven and allow it to cool slightly.

Sprinkle the tart with icing sugar for an elegant touch.

Serve warm or at room temperature, optionally with a scoop of vanilla ice cream or a dollop of whipped cream for added indulgence.