Preheat oven to 350°. Line a 9x13” pan with foil and spray with cooking spray.
Make the crust: add butter, flour, and sugar to a large bowl. Mix with a stand or a hand mixer until it becomes crumbly. (You may need to use your fingers to break up any larger chunks of butter.) Press into the bottom of the prepared pan. Bake for 15 minutes.
While the crust is baking, prepare the filling and topping.
Make the filling: Whisk pumpkin, evaporated milk, salt, and eggs in a large bowl. Whisk in brown sugar and spices. Set aside.
Make the topping: add all topping ingredients except pecans to the large bowl you used for the crust and mix with a hand mixer until crumbly, (again you may need to use your fingers to break up any large chunks of butter). The mixture will be crumbly/chunky. Stir in pecans. Set aside.
After 15 minutes, remove crust from the oven. Whisk the filling once more, then pour over crust carefully and slowly. Sprinkle topping evenly on top of filling. Bake for an additional 35-45 minutes, until topping looks set (mine took 30 minutes).Cool at room temperature and then refrigerate for at least 2 hours or overnight before cutting into squares. Store covered in refrigerator for up to 3 days or freeze in airtight bags for up to 1 month.