INSTRUCTIONS
- Preheat oven to 350°F. Line an 8×8-inch baking dish with parchment paper.
- In the bowl of a stand mixer with a paddle attachment, mix the flour, cornstarch, sugar, and salt at low speed until combined (about 5 seconds).
- Cut the cold butter into ½-inch cubes. Place the butter cubes in a small bowl and toss with ¼ cup of the flour mixture.
- Add the floured butter (with any extra flour) to the bowl of the stand mixer. Mix on low speed until the dough is light yellow in color and small crumbs (about 4 minutes).
- Remove bowl from stand mixer and use your hands to toss the mixture and rub any remaining butter bits into the flour mixture.
- Press the shortbread mixture firmly and evenly into the lined pan, smoothing it with the back of a spoon.
- Bake 35-40 minutes, or until the top and edges are lightly golden brown.
- Remove from the oven and let cool for about 5 minutes. (Leave the oven on for additional baking.)
- After cooling, press a piece of parchment paper onto the shortbread and cover it, gently holding it down with the palm of your hand. Invert the shortbread upside down onto your hand and carefully lift the pan off. Lay the shortbread flat on the countertop or cutting board.
- With a knife, slice the shortbread in half. Then, slice into fourths the other direction (giving you 8 rectangular cookies). Pierce a few holes on the top of each section with a toothpick, wooden skewer, or fork.
- Put the shortbread (still on parchment paper) onto a baking sheet and bake an additional 8 minutes to firm up. Remove from oven and let cool before serving.