Preheat oven to 350 degrees F. and line a 9×13 inch baking pan with tin foil sprayed with non-stick cooking spray.
Place cake mix, butter and egg into a large bowl, mixing to combine. Use your hands, it works much quicker 🙂 Press into prepared baking pan. Top with broken pieces of cookies.
Pour sweetened condensed milk over cookies and top with chocolate chips. Bake for 23-25 minutes, until cooked through. Remove from oven.
After 5 minutes of cooling, run a plastic knife around edges to loosen, this makes it much easier to remove from foil. Let cool completely, remove foil from pan, then cut into squares. I cut off all of the edges before cutting into squares (makes for neater squares), but do whatever you’d like!!