Preheat Oven to 150°C/300°F
Cream the Butter and Sugar. In a mixing bowl, cream the softened butter and powdered sugar until light and fluffy.
Sift in Dry Ingredients. Sift in the cornstarch and flour, mixing until just combined to form a dough.
Roll and Cut. On a floured surface, roll out the dough to a 1cm thickness and cut into 1cm x 6cm rectangles. Or to the desired shape. I made these ones into a block and cut slices of dough. Prick each cookie 3 times with a fork.
Place on a lined baking sheet and chill in the fridge for 10 minutes.
Bake for about 15-20 minutes then turn down the oven temperature to 130C/250F for 10 minutes or until lightly golden. They will be crisp and pale. (Optional: Sprinkle with caster sugar when hot out of the oven).
Cool. Let the shortbread cookies cool on the baking sheet for a few minutes before transferring to a wire rack.
