In a bowl mix the butter and sugar till creamy using a wooden spoon. In another bowl mix the flour and custard powder.

Beat the egg and add it to the butter and sugar mixture and mix well.Then add the flour and custard mixture and mix till creamy.Till soft but don't knead the dough.Shape them into medium sized balls and roll in sugar(castor)arrange them on a baking tray lined with parchment paper leaving about 2inch gap between them.

Press with a fork to make the marks and bake in a preheated oven at 180c for about 15mins.