In a large bowl, mix the evaporated milk, sugar, eggs and then add the can of pumpkin and pumpkin spice and blend together.
Spray your pan and then pour the mix into the pan. You can use a 9x13 pan or 8x8 baking pan. The 8x8 pan will be very full and you may want to place a baking sheet under it when you put it in the oven.
Open the spice cake mix and sprinkle on top of the pumpkin mixture as evenly as possible.
Melt the butter into a large pitcher and pour over the powdered cake.
Bake for 1 hour 10 minutes to 1 hour 25 minutes, or until the pie below the crust is firm.
Allow to cool before serving, the pie needs to set up like a normal pumpkin pie would (it needs to solidify) .