Preheat oven 350. Grease and flour 9x13 pan. Measure out 1 cup of dry cake mix, set aside. Place remaining cake mix, ½ cup butter and one egg in mixing bowl. Beat until fully combined. Using your fingers, gently press the batter into the pan and partially up the sides. Set aside.
For the Filling:
Combine pumpkin, evaporated milk, 1 cup sugar, 3 remaining eggs and cinnamon in same mixing bowl. Beat on low until combined. Beat again, on medium until the mixture lightens in color and texture, 1-2 minutes more. Pour filling over the crust in the pan. Set aside.
For the Topping:
Place chilled butter and the reserved cake mix in mixing bowl. Beat until crumbly, about 2 minutes. Stir in pecans. Distribute topping over the filling. Bake until the center no longer jiggles when you shake the pan and the top has browned, approx. 1 hour. Remove from the oven and cool at least 20 minutes before serving. Serve cold or warm with whipped cream. Store this cake, without the whipping cream, covered in the refrigerator for up to a week.