In a large mixing bowl, beat the butter and caster sugar. Do not cream this mixture. (see photos above)
Sift in the flour. Add the cornstarch and salt. Mix until a dough is formed. I recommend using your hands for this.
Transfer to an 8"x8" baking pan and use a butter knife or bench scraper to cut into rectangles. Use a fork to prick holes.
Chill in the refrigerator overnight. It is important for the butter to be hard right before baking.
Preheat oven to 350℉ and bake for 35-40 minutes or until the edges start to brown.
Let cool and enjoy!
