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Heat oven to 180C/160C fan/ gas 4. Put the flours in a bowl and rub in the butter until it resembles breadcrumbs. Stir in the cheese and rosemary, then add the yolk and mix in using a fork. When the mix starts to clump together, use your hands to knead to a smooth dough.
Take walnut-sized pieces of dough, roll into balls and place on one or two lined baking trays. Flatten slightly with a fork, then bake for 12-14 mins. Alternatively, roll out between sheets of baking parchment and cut into shapes, then bake as before. Cool on the baking sheet for a few mins before moving to a wire rack to cool completely. Store in an airtight container for up to a week.