Preheat oven to 350 degrees F and grease a 9x13 baking dish with nonstick cooking spray.
In a large bowl, add the 15.25 ounce box yellow cake mix, 3 large eggs, 1 cup whole milk, and ½ cup vegetable oil. Whisk until the eggs and cake mix are well combined.
Pour the cake mix into the bottom of the prepared pan and evenly spread to the sides of the pan.
Set aside and work on the pumpkin layer.
Pumpkin Layer
In a large bowl, add the 15 ounces canned pumpkin puree, ½ cup evaporated milk, ½ cup heavy whipping cream, 3 large eggs, 1 cup light brown sugar, and 1 teaspoon pumpkin pie spice. Whisk until the eggs are thoroughly incorporated.
Carefully spoon the pumpkin mixture on top of the cake batter so it doesn’t mix. Do not pour the pumpkin layer on top it will cause the pumpkin custard to sink into the batter.
Place in the preheated oven and bake for 50 minutes to 1 hour until a toothpick in just the cake layer comes out clean or with moist crumbs. To prevent the cake from overbrowning, tent the cake with aluminum foil but be sure it doesn’t interfere with the rising of the cake.
Allow the cake to cool completely before preparing the frosting.
Frosting
Add the 3.4 ounce box instant vanilla pudding mix, 1 teaspoon pumpkin pie spice, and 1 cup whole milk in a large bowl. Whisk until the pudding thickens.
Fold in thawed 8 ounces whipped topping into the pudding mixture until no white steaks are left.
Spread the frosting on the cooled cake and add sprinkles if you're using them.
Cover with plastic wrap and store in the refrigerator for at least 1 hour before serving.
Notes
Storage: Store in an airtight container or covered with plastic wrap in the refrigerator for up to 5 days. Freezing: Wrap tightly in plastic wrap and place in a freezer bag or freezer container for up to 3 months. Thaw in the refrigerator overnight before serving.