Preheat oven to 350° F. Line a baking sheet with a silicone baking mat or parchment paper.

Sift flour, sugar, cornstarch, and salt into a mixing bowl, and stir until combined.

Cut butter into small pieces. Using hands, mix the dry ingredients with the butter until a crumbly mixture forms.

Squeeze the crumbly dough into a log shape, which can be round or square; or squeeze it into a ball, then roll out your cookie dough if you plan to use cookie cutters. Cover the log completely with plastic wrap, or place the rolled out dough on a cookie sheet.

Place the cookie dough log or sheet in the refrigerator for at least 30 minutes. You can also make the dough ahead of time and bake the cookies when you’re ready.

Slice the cookie dough log into quarter-inch disks, or cut it out using your cookie cutters. If the dough is too crumbly, leave it out for a few minutes. If a cookie breaks, just push it together. The heat from your fingers will help melt the butter in the dough and form the cookie.

Place on the lined baking sheet and bake for 10-12 minutes, until the cookies are very lightly browned and hard on the edges.

Let the shortbread cookies cool for at least 5 minutes before moving.