1. Make the pastry. Beat together the margarine, caster sugar and vanilla until pale and creamy, then beat in the cinnamon, flour, cornmeal, egg yolk and 1-2 teaspoons of cold water until it comes together as a smooth dough. Wrap the dough in cling film and chill for 30 minutes.
2. Place the dough between 2 large sheets of cling film. Roll out to 5mm thick and remove the cling film. Use an 8cm plain or fluted biscuit cutter to stamp out 12 circles, then use the circles to line a 12-hole bun tin. Re-crumble any of the pastry trimmings and set aside.
3. Divide the marzipan into 36 equal-sized pieces and roll into small balls. Spoon a couple of teaspoons of mincemeat into each pastry case and scatter with the cranberries, marzipan balls and remaining pastry crumbs. Chill for 20 minutes.
4. Meanwhile, preheat the oven to 180°C/fan160°C/gas 4. Bake the pies for 25-30 minutes until golden. Cool slightly, then carefully remove from the tin. Lightly dust with icing sugar to serve.
Tip: Gluten-free pastry can be tricky to use and very crumbly, so don't worry if you have to press the pastry into the tin. Chilling the pastry for 30 minutes in the fridge will make it easier to use.