Place flour mix, baking powder, salt, cayenne pepper and butter in the bowl of a food processor. Whizz until the mixture resembles fine breadcrumbs. Add the rosemary, parmesan and cheddar and pulse to combine. Add the egg and pulse until the mixture begins to clump together.
Turn out on to a clean surface and knead gently to form a smooth dough.
Divide mixture in half.
Roll out each half to 4–5 mm between two sheets of baking paper using a little rice flour to prevent sticking. Cut in to biscuits about 7 cm x 3cm. Reroll the offcuts until all the dough has been used.
Transfer to a baking paper-lined tray and bake for 12–15 minutes until golden.
Transfer to a wire rack to cool. They will keep well in an airtight container for several days.
