Heat oven to 220C/200C fan/gas 7. Roll the pastry out on a lightly floured surface a little thinner than a £1 coin. Stamp out 12 circles about 8cm wide, keeping all the trimmings. Use the circles to line a 12-hole, non-stick bun tin. Put a small spoonful of mincemeat in each one, but be careful not to put too much, as the suet will melt and bubble out if it has no room to spare. Re-roll the pastry trimmings and cut out another 12 circles a little smaller than the last. Brush the edges of the pastry with beaten egg, then add pastry lids, pinching the two edges together. Make a small cross with a knife in the centre of each pie. The pies can now be frozen in the trays for up to 3 months and either defrosted and cooked as stated or cooked from frozen.
Brush the lids with a little more egg, sprinkle with sugar and bake for 15-20 mins until golden brown. Leave to cool slightly and serve warm.