Add the flour, granulated sugar, and salt to a food processor and pulse to combine.
Add the butter and vanilla. Pulse until the dough begins to clump together.
Press the dough into a 9-inch square baking pan. Use a bench scraper or spatula to smooth the top.
Using a fork, crimp the edges and prick the dough.
Bake for 50-60 minutes, until golden brown.
While hot, cut into squares, bars, or wedges and sprinkle with 1 tablespoon granulated sugar.
Cool completely on a wire rack before removing from the pan.
Notes
Storage: Store shortbread in an air-tight container at room temperature for up to 2 weeks, or in the freezer for up to 2 months. Baking Pan: Use an ungreased or parchment-lined baking pan. Either an 8-inch square, 9-inch square, or 9-inch round baking pan works here. The parchment isn't necessary, but can be helpful for lifting the cookies from the pan.No Food Processor? To make these cookies without a food processor, whisk together the flour, sugar, and salt in a large bowl. Then work in the butter with a pastry cutter, two forks, or your fingers until the dough begins to clump together.