Combine the flour, cocoa and caster sugar. Rub in the chilled butter until the mixture resembles coarse crumbs. (You can also do this in a food processor.) Add the milk.
Press 2/3 of the mixture into a 9-hole patty tin, over the bottom and the sides. Fill each case with mincemeat.
Roll out the remaining mixture. Cut circles to make the pie lids (or stars instead of circles). Moisten the edges of the pastry lids with a little water, then press on top of the cases in the patty tin.
Bake for 15 minutes, or until pastry is done. Cool in tins before turning out and decorating.
To decorate with chocolate drizzle, first place the cooled pies on a serving platter. Drizzle with melted chocolate. Tip: You can place the slightly cooled melted chocolate in a plastic freezer bag, then cut off one corner to squeeze out a uniform drizzle!