Preheat oven to 350° F. Line a 9 × 13 pan with parchment.
Make the crust: In a medium bowl, mix together melted butter, sugar, 1 ½ teaspoons vanilla extract, and ½ teaspoon salt. Add the flour and cornstarch, stirring until fully combined.
1 cup melted unsalted butter, ½ cup sugar, 2 ½ teaspoons vanilla extract, 1 teaspoon salt, 2 cups flour, 1 Tablespoon cornstarch
Press evenly into the bottom of the pan. Bake for 15 minutes, until edges just begin to lightly brown. Using a fork, gently prick the crust all over, being careful not to poke all the way through.
In a large bowl, whisk together pumpkin, brown sugar, eggs, evaporated milk, pumpkin pie spice, cinnamon, remaining 1 teaspoon vanilla extract, and remaining ½ teaspoon salt until smooth.
15 ounces pumpkin purée, ¾ cup brown sugar, 2 large eggs, 12 ounces evaporated milk, 2 teaspoons pumpkin pie spice, 1 teaspoon cinnamon
Pour filling over the warm crust and bake 35-40 minutes, until the center is just set.
Cool completely at room temperature for 2 hours, then chill at least 1 hour before slicing.