Preheat oven to 350 degrees and spray a 13 x 9 pan with cooking oil spray
In a bowl, whisk pumpkin, milk, brown sugar, eggs, pumpkin pie spice, cinnamon, and salt until combined
Pour mixture into pan
Sprinkle dry cake mix over the entire surface using a spoon to carefully spread it to the edges
Top with cubed butter evenly over the cake mix
Sprinkle on the pecans
Bake for 1 hour
Cool completely before cutting into squares
Refrigerate after serving
Serve with a dollop of whipped cream or vanilla ice cream if desired
