Preheat the oven to 130ºC. Line two baking trays with baking paper.
Cream the butter and icing sugar until light and fluffy. Sift the cornflour and flour together and add to the creamed mixture.
Turn onto a floured surface and knead well, pushing the mixture with your hands until it forms a smooth dough.
Divide the dough in half and roll out each half on a piece of baking paper into a circle about 1cm thick. Mark the dough into wedges and prick the surface all over with a fork. Chill for 20 minutes and then slide the baking paper onto the prepared trays. Bake for about 1 hour until a very pale gold. Cut into wedges for serving.
Form the dough into a log, wrap in greaseproof paper and chill for 10 minutes. Then cut into 5mm thick biscuits. Place on the prepared trays and prick with a fork. Bake for about 30 minutes or until pale golden.