Preheat oven according to brownie instructions.
Prepare a 9x13 baking pan by lining it with parchment paper or foil. (If using foil, spray with non-stick cooking spray. Bake according to instructions on brownie box.
While brownies are cooling, mix cookie dough.
Beat together butter and sugars until light and fluffy. Add in heavy cream and vanilla until incorporated.
Mix in four, salt and chocolate chips. Do not over mix.
Once brownies are completely cooled, spread cookie dough across the top and press down firmly to get a smooth even surface of dough.
Let cookie dough and brownie sit in the refrigerator while you make the frosting to get firm.
Place milk and butter in a microwave safe bowl and microwave in 30 second increments until butter is melted. Mix to make sure the milk and butter are combined.
Add in the cocoa powder and stir.
Slowly add in the powdered sugar and mix to combine.
Spread over the cookie dough on top of the brownie. (HINT: if the frosting is too thick to spread easily, microwave for 20-40 seconds to soften. It can be runny because it will set up thick and fudgey)