Put the flour in a mixing bowl and add a pinch of salt. Dice the butter, add to the flour and, using your fingers, crumble it until you get a mixture resembling breadcrumbs. You can instead use a food processor.
Add the sugar and egg yolk. Using a palette knife work the batter into a dough, gradually adding 1 or 2 Tbsps of cold water to it.
Form a big ball shape from the dough, wrap with clingfilm and rest in the refrigerator for about 15 minutes.
In the meantime, grease a shallow cupcake tray or patty tins and preheat the oven to 200°C.
Roll out the pastry on a lightly floured surface to the thickness of a pound coin. Cut out 12 circles with a pastry cutter (or a mug) large enough to fill the base of each of the tin's holes. Gently press the disks into the holes and fill them with about 1 teaspoon of mincemeat.
Re-roll the leftover trimmings and cut out slightly smaller disks to cover the mincemeat - or using a cookie cutter stamp out star or tree shapes and put these on top the pies.
Bake for 20-25 minutes, until the pastry is cooked through and lightly golden.
Serve warm or lukewarm, with some icing sugar dusted over them.