Preheat the oven to 350 degrees Fahrenheit and spray a 9"x13" baking dish with nonstick baking spray.
In the bowl of an electric mixer, add pumpkin puree, eggs, salt, pumpkin pie spice, evaporated milk and brown sugar and mix until completely incorporated, scraping down the sides in between.
Pour the pumpkin mixture into the prepared pan and spread it out evenly.
Sprinkle the dry yellow cake mix evenly over the top.
Sprinkle the cake mix layer with chopped pecans.
Melt the butter, then stir in 1/2 tsp. pumpkin pie spice completely. Pour the melted butter mixture over the top evenly.
Bake for approximately 50-55 minutes, or just until set. Let it cool mostly, then serve with whipped cream or whipped topping on each piece.