Preheat the oven to 200C (180C for a fan oven).
Place the rice flour, xanthan gum, nut butter and coconut butter in a food processor and blend until the mixture resembles breadcrumbs.
Add the egg and blend again.
With the mixer running add one tablespoon of water at a time until the pastry just starts to come together.
Lightly knead the pastry until combined, then roll out about 3-4mm thick on a well-floured surface.
Use a pastry cutter to cut 12 rounds, each slightly bigger than the indents on your tart tin.
Carefully press the pastry rounds into the non-stick tart tin and then fill each one with a rounded teaspoon of the mince meat – be careful not to overfill them otherwise the mincemeat will boil over the side whilst in the oven.
Cook for 10 minutes, allow to cool slightly in the tin, then transfer to a cooling rack.