Grease bottom only of 9x13 pan. Reserve 1 cup cake mix for topping. Combine remaining cake mix, butter, and egg. Press into pan. Prepare filling by combining all ingredients until smooth. Pour over crust. For topping combine all ingredients. Sprinkle over filling. Bake at 350 degrees for 45-50 minutes until knife inserted near center comes out clean. If desired serve with whipped topping. *Tip: For use with 1 pound can solid-pack pumpkin, add 2 1/2 teaspoons pumpkin pie spice and 1/2 cup firmly packed brown sugar. Prepare as directed above. High altitude-5200 feet: Add 2 tablespoons flour to cake mix. Bake at 375 degrees for 45-50 minutes.