Measure the flour into a medium bowl.
Cut cold butter into small pieces and add to the flour.
Mix both with your fingertips or a cake mixer or a food processor until the mixture resembles fine breadcrumbs. Make sure there are no solid bits of butter left unmixed.
Add the powdered sugar and salt and combined well. At this stage, the mixture would still look like breadcrumbs.
Next, add the egg and vanilla extract. Mix the ingredients until a dough is formed. Do not overmix, suffice if all the ingredients come together into a smooth ball.
Set it aside for about 10 minutes to rest. Once rested, knead lightly and divide the dough into 15 to 16 portions.
Form each portion into round balls.
Flatten each ball with your fingers to form a round disc.
Place the disc into the tart mold and press it down gently to follow the shape of the mold. In doing this, pay attention to the thickness of the pastry to ensure it is consistent for an even baking.
Trim off the excess at the edges with a sharp knife or press it down with your fingers to flatten it.
Use a fork to poke in the center. This will avoid the centers from puffing up as they bake.
Place the shells in a pre heated oven and bake for 15 minutes at 175 degrees Celsius until they turn golden brown. Do not over bake.
Remove the pastry from oven and let them cool slightly before removing the casings. Let the shells cool completely before using. The shells can be baked a few days in advance and stored in an airtight container until ready to use.