Preheat oven to 350 degrees. Line a 9×13 baking dish with parchment paper and set aside. In a medium bowl, combine the butter, sugar and egg. Mix until creamy. Add flour and salt and stir until combined. Using your fingers (flour them, if needed), press the dough evenly into the bottom of the prepared pan. Bake in the preheated oven for 15 minutes.
In a separate bowl, combine the eggs and sugar. Mix well. Add the evaporated milk, pumpkin, pumpkin pie spice and salt. Mix until combined. Pour over the crust and bake for an additional 40-45 minutes, or until center is no longer jiggly.
Let cool, cut into squares and serve with whipped topping (if desired).