Bake cake per instructions on back of cake mix. (I make my cake a bakery style by substituting melted butter for the oil and milk for the water.) It makes such a rich and fluffier cake.
Allow cake to cool after baking. Using the back end of a wooden spoon or other large utensil make large holes through out cake. You will need the holes to be able to fit blueberries. Make a lot of holes.
In a small bowl whisk together 1 cup of blueberry pie filling and sweetened condensed milk. (If you want to use homemade blueberry pie filling, check out my simple recipe in my recipes, it's so delicious.)
Pour the mixture into the holes all throughout the cake. Using a knife or an offset spatula smooth out the filling to make sure most goes into the holes.
Spread the cool whip topping evenly over cake. Dollop 2 TBS of pie filling onto the whip topping and swirl together to get a pretty color on top.
Refrigerate cake for 4 hours or overnight. The longer it sits the more delicious it is.
