The Unusual Butter Hack For Better, Easier Shortbread

Name: The Unusual Butter Hack For Better, Easier Shortbread
Prep time: 4 min
Cook time: 40 min
Total time: 44 min
Yield: 6
Ingredients: 255g all-purpose flour (9 ounces; 2 cups); 255g white whole wheat flour (9 ounces; 2 cups), see notes226g cornstarch (8 ounces; 2 cups); 170g golden caster, caster, or superfine sugar (6 ounces; about 3/4 cup plus 2 tablespoons), plus more for topping (see notes); 1/2 teaspoon Diamond Crystal kosher salt; for table salt, use half as much by volume454g unsalted butter (1 pound; 2 cups)