Preheat your oven to 350°F (175°C). Prepare a 9x13 inch baking pan by greasing it lightly or lining it with parchment paper for easy removal of the brownies after baking.
In a large mixing bowl, combine the melted butter and granulated sugar. Use a whisk or spatula to stir the mixture until it becomes smooth and fully integrated.
Add the eggs one at a time to the butter-sugar mixture, mixing well after each addition to ensure everything is well combined. Stir in the vanilla extract until the mixture is uniform.
In a separate bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking powder, and salt. Gradually fold this dry mixture into the wet ingredients, blending gently until just combined—be careful not to overmix.
Carefully fold in the mint chocolate chips and the chopped Oreo cookies, ensuring they are evenly distributed throughout the batter for a delightful surprise in every bite.
Pour the brownie batter into the prepared baking pan, using a spatula to spread it out evenly and smooth the top.
Place the pan in the preheated oven and bake for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs, indicating the brownies are perfectly fudgy.
Once baked, allow the brownies to cool in the pan on a wire rack for at least 15 minutes before carefully transferring them to the rack to cool completely.
For an optional indulgent finish, drizzle chocolate ganache over the cooled brownies, letting it set slightly before slicing into squares.
Notes
For an indulgent finish, drizzle chocolate ganache over the cooled brownies.