Heat the oven to 180C or 350F.
Add the flour and butter to a mixing bowl and rub it together with your fingertips until the mixture looks like breadcrumbs.
Then sift in the icing sugar and add the salt and egg yolk and continue to rub together with your hands until combined.
Add a little water (one teaspoon at a time) if the pastry is too dry to form into a ball.
Roll the dough into a ball, wrap in cling film and place it in the fridge for a least 30 minutes.
Place the dough onto a lightly floured surface and roll out until around 3-4mm (⅛ inch) thick.
Use a cutter to cut the dough into circles and place them into tartlet cases or a tartlet tin.
Repeat these steps until all the dough has been made into tartlet shells.
Prick the bottom of each tartlet shell with a fork a few times.
Place the tarlet shells into the middle of the oven and bake for 15-20 minutes until they begin to brown.
Allow them to cool in the tin or cases for 10 minutes and transfer to a wire rack to cool completely.