Using a mixer combine butter, icing sugar and cornflour together in a large bowl.
Add in flour 1/2 cup at a time until it is all incorporated. The mixture should be thick and crumbly.
Turn out the dough onto a clean bench top and press together until you can form it into a ball.
Roll out your dough ball into a log about 5cm thick. Use a piece of baking paper to wrap it and pull it tightly. Set in the fridge for at least 30 minutes.
Preheat oven to 150 degrees (fan bake).
When you are ready to bake, slice your shortbread into 1cm rounds. Lay on a lined baking tray leaving a little space between. Bake for 10 minutes. When the biscuits are done they will still be soft with firmer edges. They will firm up fully as they cool.
