1. Sift together flour, sugar, and salt into a bowl. Place butter into the bowl of an electric mixer fitted with the paddle attachment. Mix on medium-high speed until fluffy, 3 to 5 minutes, scraping down sides of bowl. Gradually add flour mixture; beat until pale and fluffy, about 2 minutes.

2. Preheat oven to 300 degrees, with rack in upper third.

3. Using plastic wrap, press dough into a buttered 10-inch fluted tart pan with a removable bottom. With plastic on dough, refrigerate 20 minutes. Remove plastic wrap. Cut dough into eight wedges with a paring knife. Using a wooden skewer, prick all over at 1/4-inch intervals.

4. Bake until golden brown and firm in center, about 1 hour. Transfer pan to a wire rack. Recut shortbread into wedges; let cool completely in pan. Cookies can be stored in an airtight container at room temperature up to 2 weeks.