Preheat oven to 200°C /180°C fan/gas 4. Take the pastry out of the packaging 10-15 minutes before you are ready to use it. Unroll the pastry and using a 7.5cm cutter cut out 12-16 discs and line the base of the holes of a 12-16 muffin tin. Cut out the same number of smaller 6cm discs (using either a fluted or star shaped cutter) for the lids and set aside. Re-roll the offcuts until you have enough lids.
Drop 2 teaspoons of mincemeat into each case, lightly moisten the undersides of the pastry lids with water and use to top tarts, pressing gently at the edges to seal.
Make a tiny hole in the top of each pie with the tip of a sharp knife (to allow any steam to escape), brush with water, sprinkle with the caster sugar and bake for 15-20 minutes or until golden brown.
Sprinkle with a little more sugar and allow to stand in the tin for 2-3 minutes before carefully transferring to a cooling rack. Once completely cool, these tasty festive treats can be put in an airtight container and frozen for up to a month. Simply defrost at room temperature for an hour. To serve warm, just pop in the oven for 3-4 minutes at 180°C /160°C fan/gas 3.