In a food processor, whizz together the flour, sugar and butter until you get fine crumbs (or rub together with your fingers). Add the orange zest and juice. Whizz again for a few more seconds until you get a smooth dough.
Form a big ball from the dough, wrap it in clingfilm and rest for 30 minutes in the refrigerator.
Heat the oven to 190C. Grease a 12-hole, non-stick shallow muffin or bun tin.
Finely chop the chestnuts.
Roll out the pastry on a lightly floured surface to 3 mm thickness. Cut out circles with a pastry cutter (or a mug), large enough to cover the tin holes (about 8 cm diameter) then press the pastry disks into them.
Fill each base with chestnuts and mincemeat.
Re-roll the trimmings to the same thickness and stamp out small stars for the tops. Dampen the edges with water, then press them lightly on top of the edge of the pies.
If you'd like the pies to have a shiny glaze, lightly beat an egg, then brush the stars and the edges of the pies with it.
Bake in the oven for 15-20 mins until golden. Cool for a few minutes, then move them to a wire rack.
Dust with icing sugar just before serving.