I think I got this recipe from another blog but I don't remember whose it was...so just know that I'm not trying to steal a recipe, but sharing what's yummy and telling you it's not originally mine.
1 (15 oz) can pumpkin
1 c. evaporated milk
1 c. sugar
1 tsp. vanilla
1 tsp. ground cinnamon
1 pkg butter recipe yellow cake mix (Duncan Hines or Betty Crocker are ones I've used)
1 c. chopped pecans (optional)
2 sticks butter, melted
Stir together first 5 ingredients (it will be very runny). Pour into greased 9x13 baking dish.
Sprinkle cake mix evenly over mixture. Sprinkle on pecans (again, optional). Drizzle butter over everything.
Bake at 350 degrees for 1 hour, or until golden brown. Let stand 10-15 minutes before serving.
Good with whipped cream. Good warm or cold.