18 oz box brownie mix, plus ingredients called for on the box (usually eggs, oil, and water)
Optional: flaky sea salt for sprinkling on top after baking
Step-by-Step Instructions
Prepare the pan and cookie layer
Preheat your oven to 350°F (175°C) or to the temperature recommended on your brownie mix box if it differs slightly.
Line a 9×9‑inch baking pan (or similar size) with parchment paper, leaving overhang on the sides so you can lift the brownies out later. Lightly grease the parchment for extra insurance.
Press the chocolate chip cookie dough evenly into the bottom of the pan to form a solid layer. Take your time to spread it into the corners; it should be fairly even in thickness so it bakes uniformly.
Add the Oreo layer
Arrange the 16 Oreo cookies in a single layer on top of the cookie dough. You can do four rows of four cookies. Gently press each cookie just slightly into the dough so they stay in place but remain mostly whole.
Mix and pour the brownie batter
Prepare the brownie mix according to the package directions, using the eggs, oil, and water listed on the box. Stir until just combined; overmixing can make brownies tough instead of fudgy.
Pour the brownie batter evenly over the Oreo layer, using a spatula to coax it into the corners and fully cover all of the cookies. Tap the pan gently on the counter to release any air bubbles.
Bake the slutty brownies
Bake in the preheated oven for about 35–45 minutes, depending on your pan and brownie mix. Because you have three layers, these bars often need a bit longer than a plain brownie—start checking around 30 minutes.
The brownies are done when the edges are set and a toothpick inserted into the center comes out with mostly moist crumbs and maybe a little fudgy batter, but not completely wet. The center should no longer jiggle.
If you like a sweet‑salty contrast, sprinkle a tiny pinch of flaky sea salt over the top right after the pan comes out of the oven.
Cool and slice
Let the slutty brownies cool completely in the pan on a wire rack. This can take an hour or more but is worth the wait; slicing too early will make the layers messy and the brownies very gooey.
Once cool, use the parchment overhang to lift the whole slab out of the pan. Place it on a cutting board and use a sharp knife to cut into bars, wiping the knife clean between cuts for sharp edges that show off all three layers.
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