Insanely Naughty Pumpkin Cake

My favorite fall dessert, I saw this on Good Things Utah

Crust:
1 box yellow cake (set aside 1 cup that will be used for the topping)
½ cup melted butter
1 egg
Mix cake mix, melted butter, and 1 egg well. Pour and press into lightly greased cake pan.

Filling:
3 c. Pumpkin
2 Eggs
1 ½ c. Sugar
1 Tsp. Salt
1 ½ Tsp Cinnamon
1 Tsp. Ginger
12 oz can Evaporated Milk
Mix Pumpkin, 2 eggs, sugar, salt, spices, and evporated milk. Pour over crust mix in pan.

Topping:
1 c. cake mix (reserved)
¼ c. Sugar
¼ c. Butter
3 Tbsp Flour
Mix these until crumbly. Sprinkle over pumpkin mixture.
Bake at 350 for 1 hour. Cool and serve with whipped topping.