Makes around 15 biscuits
1 Whip the butter and sugar in a mixer until light and fluffy, then gently and carefully sift in the flour and cornflour (not whilst the machine is on).
Fold in the flour, being careful not to overmix at this stage.
2 Roll the dough into 2 sausage shapes, about the width of a £2 coin (1 and a 1/2 inches). Wrap in clingfilm and leave in the fridge overnight.
3 Using a sharp knife, cut the dough into 4mm thick discs and lay on a baking tray lined with parchment and bake in pre-heated oven, 135C-150C/Gas Mark 1-2 for 45 minutes, or until they start turning golden at the edges.
Allow to cool, then dredge with extra sugar.