Pumpkin Pie Dump Cake

Preheat oven to 350º F and lightly grease a 9×13-inch baking dish with butter or non-stick spray.
In a medium bowl, whisk together pumpkin purée, evaporated milk, eggs, sugar and pumpkin pie spice until smooth and fully combined.
Pour mixture into greased baking dish.
Working in an even layer, sprinkle dry cake mix evenly over pumpkin mixture.
Optional: sprinkle nuts over cake mix.
Cut butter into thin pats and top cake mix with them, covering as much of the surface of the cake as possible.
Place in oven and bake for 55-60 minutes, or until almost set in the center.
Remove from oven and let cool at least 30 minutes before serving.