Cream the butter and both sugars in a large bowl with an electric mixer on medium speed for 3-5 minutes. Add the eggs and vanilla and mix well to thoroughly combine.
In a separate bowl, whisk together the flour, baking soda and salt, then slowly incorporate with the mixer until the flour is just combined.
Fold in chocolate chips.
Spread the cookie dough in the bottom of a 9 × 13 inch baking dish that's been lined with parchment paper and sprayed with cooking spray.
Top with a layer of Oreos.
Mix together brownie mix according to directions on the box, adding an optional ¼ cup of hot fudge topping to the mix.
Pour the brownie batter over the cookie dough and Oreos.
Bake at 350℉ for 35-45 minutes.
Cool for a few minutes before slicing.
You can serve these warm or cold.
Notes
We like to top with ice cream and hot fudge topping.