Line a 9x13-inch metal baking pan with parchment paper. Set aside.
In a large mixing bowl, cream together 1 cup granulated sugar 2 cups salted butter, and 1 tablespoon vanilla bean paste for 2 minutes, scraping down the sides of the bowl about halfway through.
In a separate, large mixing bowl, whisk together 5 cups all-purpose flour, ⅓ cup powdered sugar, 2 tablespoons cornstarch, and ¼ teaspoon salt.
Add the flour mixture to the butter mixture in 3 parts, mixing between each addition just until incorporated. The dough will be mixed but slightly crumbly.
Transfer the dough to the prepared baking pan and press it evenly into the bottom of the pan.
Prick the surface of the dough all over with a fork. Pricking the shortbread frees steam while baking and prevents air bubbles.
Chill the shortbread in the refrigerator for 30 minutes.
With 15 minutes left of chilling, preheat the oven to 325°F.
After chilling, bake for 40 to 45 minutes until the tops and edges of the shortbread should be just turning golden brown.
Immediately after coming out of the oven, sprinkle 2 tablespoons granulated sugar over the top of the shortbread.
Transfer the pan to a wire rack to cool, then use a sharp knife to gently cut the shortbread into squares in the pan. Don't cut too hard because you want to try and avoid cutting the parchment or damaging the pan. Shortbread is easier to cut when warm.
Let the shortbread cool completely before lifting it out of the pan and enjoying.