Prepare the Cake Batter:
In a large mixing bowl, combine the yellow cake mix and pumpkin puree. Mix until a smooth batter forms, making sure there are no lumps.

Bake the Cake:
Pour the batter into a greased 9×13-inch baking dish. Bake at 350°F (175°C) according to the directions on the cake mix box, typically for 23-28 minutes, or until a toothpick inserted into the center comes out clean.

Cool the Cake:
Once the cake is baked, remove it from the oven and let it cool for about 10 minutes.

Poke Holes in the Cake:
Using the end of a wooden spoon, poke holes all over the top of the cake. These holes will allow the sweetened condensed milk to soak into the cake.

Add Sweetened Condensed Milk:
Pour the sweetened condensed milk over the entire cake, making sure to fill the holes and cover the surface. The milk will seep into the cake, adding moisture and sweetness.

Refrigerate the Cake:
Place the cake in the refrigerator and let it chill for 30 minutes to allow the milk to absorb fully.

Top the Cake:
After the cake has chilled, remove it from the refrigerator. Spread the Cool Whip evenly over the top of the cake. Sprinkle the Heath bits generously over the Cool Whip layer.

Drizzle with Caramel:
Finish the cake by drizzling caramel sundae sauce over the top. Adjust the amount based on your sweetness preference.

Chill Before Serving:
Refrigerate the cake for 3-4 hours or overnight to allow the flavors to meld together.