In a light-colored skillet over medium heat, melt cubed unsalted butter until it turns a nutty brown color, about 5-8 minutes. Once browned, remove from heat and let it cool slightly.

In a large mixing bowl, combine the cooled brown butter with dark brown sugar and granulated sugar, whisking until smooth and glossy. Then, add a large egg, mixing well until fully incorporated.

In a separate bowl, whisk together all-purpose flour, baking soda, and fine sea salt until well combined. Gradually add this mixture to the wet ingredients, stirring gently until just combined—avoid overmixing.

Gently fold in the chopped dark chocolate and crumbled Oreos, ensuring they are evenly distributed throughout the cookie dough.

Cover your cookie dough with plastic wrap and chill in the refrigerator for 30 to 60 minutes.

Preheat your oven to 350°F (180°C) while the dough chills. Scoop rounded tablespoons of cookie dough onto a lined baking sheet, spacing them about 2 inches apart. Bake for 10-12 minutes.

Let the cookies cool on the baking sheet for about 5 minutes before transferring to a wire rack to cool completely.