Spray a 9-inch fluted tart pan with a removable bottom with nonstick cooking spray; set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream together butter and sugar. Stir in vanilla. With mixer on low speed, slowly add flour. Mix until well combined.
Evenly spread cookie dough into prepared tart pan. Refrigerate until firm, at least 2 hours and up to overnight.
Preheat oven to 325 degrees. Sprinkle shortbread with sanding sugar. Using a 2-inch round fluted cookie cutter, make a shallow cut in the center of the dough. Using the tines of a fork, score dough from the edge of the circle in the center toward the edge of the pan into 12 equal wedges.
Transfer tart pan to oven and bake until light brown and a toothpick inserted into the center of the shortbread comes out clean, 50 to 60 minutes. Immediately re-score circle and wedges with cookie cutter and the tines of a fork. Transfer to a wire rack and let cool 1 hour. Remove shortbread from tart pan and let cool completely. Cut into wedges with a serrated knife along the scored lines.