Lemon and lime biscuits

* Preheat the oven to Gas Mark 6/200 ° C / 400 ° F. Sift the flour into a bowl, add the margarine and rub in using your fingertips until the mixture resembles bread crumbs. Stir in the sugar, lemon and lime zest.

* Add a tsp of lemon juice and mix to a stiff dough. Add a little more juice if the mixture is too dry. On a lightly floured surface roll out to 1cm thickness and cut 12 x 6cm fluted circles. Re-roll and cut any remaining dough. Place on a non-stick baking sheet, sprinkle with the reserved sugar and cook for 10 mins until golden. Leave on the tray for 5 minutes before transferring to a wire rack to cool. Store in an airtight container for up to 3 days.