Prepare the Cookie Dough

1. Preheat Oven: Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
2. Mix the Brownie Dough: In a large mixing bowl, combine the brownie mix, melted butter, eggs, and vanilla extract. Stir until smooth and well combined.
3. Add Dry Ingredients: In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add this mixture to the wet ingredients, stirring until just combined.
4. Form the Cookie Dough: Using a spoon or cookie scoop, portion out a heaping tablespoon of cookie dough. Roll it into a ball and flatten it slightly.

Assemble the Oreo Brownie Cookies

1. Place the Oreo: Place one whole Oreo cookie in the center of each flattened dough ball. Gently press the dough around the Oreo to completely enclose it.
2. Shape and Bake: Place the dough balls on the prepared baking sheets, spacing them about 2 inches apart. Bake in the preheated oven for 10-12 minutes, or until the edges are slightly firm but the centers are still soft.
3. Cool: Let the cookies cool on the baking sheets for about 5 minutes before transferring them to a wire rack to cool completely.