Prep. Preheat the oven to 425°F. Butter a 9x13-inch baking dish or line with parchment paper.
Shortbread Crust
Cut in butter with flour. In a large bowl, stir together 1 1/2 cups flour and 1/2 cup sugar. Cut in 3/4 cup cold butter with a pastry cutter (you could also do this in a mixer or food processor) until crumbly but not become a dough. Press into the baking dish.
Pumpkin Pie
Pumpkin filling. In a large bowl, beat 4 large eggs. Stir in 2 teaspoons vanilla, 1 1/2 cups sugar, 2 teaspoons pumpkin pie spice, 1 teaspoon cinnamon, and 1 teaspoon salt until combined. Stir in 2 cans pumpkin. Gradually add 2 1/2 cups evaporated milk and mix until smooth. Pour filling on top of the shortbread crust.
Bake. Bake 40 minutes. Cover with foil if starting to get too brown on top. Reduce the temperature to 350°F and cook an additional 20 to 30 minutes, or until a toothpick inserted in the center comes out clean.
Cool and serve. Let cool completely, about 2 hours. You can place in the refrigerator after about 1 hour to cool them faster. Slice and serve with whipped cream on top.
Notes
Storage: Store in a covered container up to 5 days in the refrigerator.Variation: If you prefer a sturdier crust (this shortbread is a softer crust), you could use a graham cracker crust. I would just double this graham cracker crust recipe.