Preheat oven to 350 degrees and coat a 9x13" baking dish with non-stick spray.
Prepare cake batter according to the directions on the back of the box and pour in prepared pan.
In a large bowl, whisk together the pumpkin puree, evaporated milk, heavy cream, eggs, brown sugar, and pumpkin pie spice, until smooth.
Gently pour the pumpkin mixture on top of the unbaked cake batter.
Carefully place the pan in oven and bake for 50-60 minutes at 350°F. Check cake with a toothpick to ensure doneness.
To Make the Frosting:
In a large bowl, combine the pudding mix, pumpkin pie spice, and milk. Whisk together until the mixture starts to thicken.
Fold in the whipped topping until combined and fluffy.
Scoop frosting onto the baked and cooled cake, spreading evenly.
Refrigerate until ready to serve.
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Notes
Nutrition information is an estimate.Prep Tips:
Pumpkin - Be sure to use pumpkin puree or 100% real pumpkin for this recipe, NOT pumpkin pie filling. We are essentially making our own pumpkin pie filling, so you want to start with plain pumpkin. Pumpkin pie filling already has sweeteners and spices added, so that would be too much in this recipe.
Whipped Topping - For the frosting, it is important to use whipped topping versus real dairy whipped cream. Whipped topping, such as Cool Whip, is made with stabilizers that will help it keep its shape and hold up for a couple days in the fridge, if needed. Whipped cream will "fall" and become more liquid over time.
Storage - Keep cake covered and in the fridge until you're ready to serve. Leftovers can be stored in the refrigerator for 2-4 days.