Preheat oven to 350 degrees.
In a large mixing bowl mix together pumpkin, pumpkin pie spice, evaporated milk, eggs, and sugar.
Pour into greased 9 x 14 in pan or 2.5 quart baking dish.
Sprinkle dry cake mix over the top of pumpkin mixture.
Drizzle butter over the top of cake mix.
Top with walnuts.
Bake for 1 hour or until a knife inserted into the middle comes out clean.
Serve with Cool Whip or ice cream.
