Heat the oven to 200°C (180°C in a fan oven), 400°F, gas 6.
Mix together the butter and the sugar until creamy. Sieve in the flour and the rice flour and knead into a smooth dough. Finally knead in the cranberries, then wrapped the dough in clingfilm and chill for approx. 30 minutes.
On a floured work surface, roll the dough out approx. 4 mm thick and cut out heart shapes. Sprinkle with some sugar and place on a baking tray lined with grease-proof paper.
Bake for 10-15 minutes until slightly golden. Remove from the oven and the tray and leave to cool.