from Pioneer Woman)
Preheat oven to 325 degrees.
Cream butter and sugar together. Sift in flour and cornstarch and blend together using a pastry cutter or using a fork until the ingredients all come together.
Form dough into a ball, place in Zip-loc bag, and refrigerate 20 minutes.
Roll onto a lightly floured surface and cut into rounds. Place on a cookie sheet lined with parchment paper or a baking mat.
Bake for 20 minutes. Do not allow shortbread to brown; the edges should have the faintest golden tinge.