Shortbread Cookies

Cooking spray, for greasing

1 cup unsalted butter, softened

3/4 cup powdered sugar

1 1/2 teaspoons kosher salt (preferably Diamond Crystal)

1 teaspoon pure vanilla extract

2 cups all-purpose flour (about 8 1/2ounces)

2 tablespoons cornstarch

Preheat oven to 350°F. Grease a 13- x 9-inch rimmed baking sheet with cooking spray. Line bottom and sides with parchment paper, leaving a 1- to 2-inch overhang on short sides.

Beat butter, sugar, salt, and vanilla on medium speed in a stand mixer fitted with the paddle attachment until smooth and well combined, about 1 minute. (Do not beat until light and fluffy.) Reduce speed to low, and gradually add flour and cornstarch. Continue to beat until well combined and a dough just forms, 30 seconds to 1 minute, stopping to scrape down sides and bottom of bowl as needed.

Roughly crumble dough evenly onto prepared baking sheet. Place a sheet of plastic wrap directly on the surface of the dough; press dough into an even layer. Remove and discard plastic wrap. Using a paring knife, cut dough into 36 bars (about 3 x 1 inch each), cutting all the way through dough to parchment paper. Gently prick dough all over using a fork.

Bake until golden brown and center is set, 30 to 35 minutes. Remove from oven; while shortbread is warm, cut along score marks. Let cool completely before serving, 40 minutes to 1 hour.