How to Make It
Preheat the oven to 350°. In a food processor, combine the flour, sugar and salt. Add the butter and vanilla and pulse until evenly moistened. Turn the crumbs out onto a large piece of parchment paper and press into a disk.
Cover with another sheet of parchment paper and roll out the dough to a rough 8-by-11-inch rectangle. Discard the top sheet of parchment. Trim the edges to form a 7-by-10-inch rectangle. Slide the dough along with the parchment onto a large baking sheet. Using a straight edge and a sharp knife, score the dough into 24 bars. Poke the dough all over with a fork and freeze until firm, about 10 minutes.
Bake the dough until golden, about 25 minutes. While the shortbread is still warm, cut it into bars. Let cool before serving.