To make the shortcrust pastry, begin by cutting the vegan butter into cubes.
Combine the flour and salt in a food processor and add the butter.
Pulse until the mixture resembles coarse breadcrumbs and the butter is evenly distributed.
With the processor on low, add the water one tablespoon at a time until the mixture just comes together.
You may not need all the water.
Remove the dough, shape it into a flat circle, wrap it tightly, and refrigerate for at least 30 minutes.
Once chilled, lightly flour a surface, remove the dough, and reserve ¼ for decoration.
Roll out the remaining dough to about 1.5 inches larger than the diameter of your 20cm tart tin.
Carefully lift it with a rolling pin and drape it over the tin, gently pressing it into the corners.
Trim any excess, leaving about a 1cm overhang and set aside.
Roll out the reserved dough and cut decorative shapes like holly leaves or stars.
Pour the filling in the lined dough in tin.
Place them on a parchment-lined baking sheet.
Refrigerate both the tart and decorations for the remaining 20 minutes.
After chilling, line the tart case with baking parchment, fill it with baking beads or uncooked rice, and bake for 15 minutes.
Remove the beads and return the tart to the oven for another 5 minutes, ensuring it doesn’t brown too much.