In a bowl, mix together the brown butter, brown sugar, and white sugar for the cookie dough. Add the egg, egg yolk, and vanilla extract, and mix until combined. Stir in the flour and baking soda, then fold in the chocolate chips. Set aside.
In a separate bowl, whisk together the sugar, eggs, vegetable oil, and vanilla extract for the brownie batter. Add the cocoa powder, flour, and salt, mixing until a smooth batter forms. Fold in the chopped dark chocolate.
Line a square baking pan with parchment paper. Press about two-thirds of the chocolate chip cookie dough into an even layer at the bottom of the pan.
Place a single, even layer of whole Oreos on top of the cookie dough base.
Pour the brownie batter over the Oreos, using a spatula to spread it evenly and cover the cookies completely.
Break the remaining cookie dough into small pieces and scatter them over the top of the brownie batter, along with a few broken Oreos.
Bake in a preheated oven at 350°F (175°C) for about 35 to 40 minutes, or until the edges are set. Let cool completely before slicing into squares.
Cook it hands-free.
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