- 1 cup (2 sticks) unsalted butter
- 1/2 cup powdered sugar
- 2 cups all-purpose flour, sifted
- 1/4 teaspoon kosher salt
- Preheat oven to 300°F. Melt butter in a small skillet over medium heat and cook, stirring often, until milk solids begin to brown, about 6 minutes (do not burn). Strain through a fine-mesh sieve into a medium bowl. Chill until just firm, about 30 minutes.
- Using an electric mixer on medium-high speed, beat brown butter and powdered sugar in a large bowl until pale and creamy, about 2 minutes. Reduce speed to low and gradually beat in flour and salt, scraping down sides of bowl as needed, just to blend (do not overwork dough).
- Transfer dough to a sheet of parchment. Form dough into a rectangle. Place second sheet of parchment over dough. Roll out dough to a 8×6″ rectangle about 1/2″ thick.
- Remove top sheet of parchment. Transfer dough on parchment to a rimmed baking sheet. Using a fork, pierce dough all over, spacing 1″ apart. Bake shortbread, rotating halfway through, until golden brown and firm to the touch, 55–65 minutes.
- Cut shortbread lengthwise into 1″ strips on baking sheet while still warm. Cut each strip crosswise into thirds. Let cool completely.