Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan, or line it with parchment paper, leaving an overhang for easy removal.

Prepare the Chocolate Chip Cookie Layer: In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract. In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Stir in the chocolate chips. Press this cookie dough evenly into the bottom of the prepared baking pan.

Create the Oreo Layer: Arrange the Oreo cookies in a single layer over the cookie dough. You may need to break some to fit. Don't worry if there are small gaps; the brownie batter will fill them.

Make the Brownie Layer: Melt the butter and unsweetened baking chocolate together in a heatproof bowl set over a saucepan of simmering water (or in the microwave in 30-second intervals, stirring in between). Stir until smooth. Remove from heat and whisk in the sugar. Beat in the eggs one at a time, then stir in the vanilla extract. Gradually mix in the flour and salt until just combined. Pour the brownie batter evenly over the Oreo layer, spreading it to cover completely.

Bake the Slutty Brownies: Bake for 30-40 minutes, or until a toothpick inserted into the center comes out with moist crumbs attached (not wet batter). Be careful not to overbake, as you want a fudgy texture.

Cool and Serve: Let the brownies cool completely in the pan on a wire rack before cutting into squares. This is crucial for clean cuts and the best texture.