Preheat oven to 350 degrees F (175 degrees C). Spray a 9x13-inch baking dish with Non-Stick Baking Spray (to taste). Set aside.
In a medium mixing bowl, combine the Yellow Cake Mix (1 box), Egg (1), and Unsalted Butter (1/2 cup) for the crust. Set 1 cup aside.
Use a large spoon to spread the crust into the bottom of the baking pan or press it evenly with your fingers.
In a medium mixing bowl, combine the Canned Pumpkin Pie Mix (3 cup), Egg (2), and Milk (2/3 cup) for the filling.
Pour filling over crust and spread out evenly.
In a small mixing bowl, combine the 1 cup of reserved cake mix, Granulated Sugar (1/4 cup), Ground Cinnamon (1 teaspoon), and Unsalted Butter (1/4 cup). Sprinkle evenly over the filling.
Bake for 45 to 50 minutes.
Allow the dessert to cool for about around 20 minutes, and then store in the fridge for a couple of hours before serving. Bars will be tasty at room temperature, but are best served COLD.
Serve with some type of Whipped Topping (to taste).