Prepare box of cake mix according to package instructions, then pour into a lightly greased 9"x13" cake pan. DO NOT BAKE. Set aside.
In another bowl whisk together the ingredients for the Pumpkin Pie (pumpkin, evaporated milk, cream, eggs, brown sugar, and pumpkin pie spice), until smooth. Slowly pour the pumpkin pie mixture all over the cake mix.
Carefully place cake into the oven and bake for 50-60 minutes or until the center is no longer jiggly, and a toothpick inserted into cake mix comes out clean. NOTE: The cake might be slightly darker than normal, but still tastes great. Let cool to room temperature.
Make the frosting: Place the vanilla pudding mix into a large bowl, add the pumpkin pie spice and pour in the cold milk. Whisk until combined and starting to thicken. Gently fold in the Cool Whip until it's completely combined. Spread on top of the cooled cake.
You can serve now, or chill the cake, and serve when chilled. Either way tastes great. Enjoy!
Before baking the cake, you can place it on top of a rimmed baking sheet just in case any of the cake spills over the edge of the pan while baking.UPDATE:
After you are done baking the cake, it may look like it did not settle into layers, but it has! Frost it, cut it, and marvel at it's awesomeness.