In a food processor with a steel blade, place the flour, butter, powdered sugar, vanilla, and salt, then process until a crumbly mixture is obtained.
Add the egg and continue to process until the dough lumps are formed.
Transfer the dough to a lightly floured work surface and form a disc shape.
Wrap in plastic wrap and cool in the refrigerator for an hour.
On a floured surface, roll out the dough to a 3-4 mm thick sheet and set aside the baking pan, making sure to create a right angle between the side and the base, ensuring that the edges remain high.
Stab the dough with a fork.
Freeze the dough inside the pan for an hour.
Set the oven to 170°C / 350°F fan.
Place a sheet of heat resistant nylon or crumpled baking paper on the dough and fill with dry beans/chickpeas or special weights for baking. (This is known as “Baking blind" and is the process of baking a pie crust or other pastry without the filling.)
Bake blind for 13 minutes.
Remove the weights from the dough and continue baking for 13 more minutes.
Cool in room temperature.
Cut the chocolate to small pieces and place in a bowl. Heat the double cream in a pot until it start boiling - do not let it boil hard. Pour the cream on the chocolate and let it sit for 3 minutes. Mix the chocolate until it all melts and dissolves with the cream.
Pour the chocolate batter on the baked dough and keep in the refrigerator for 2 hours for stabilizing.
Decorate with coconut flakes, chocolate candies, sprinkles etc.