Melt unsalted butter in a microwave-safe bowl for about 30 seconds. Let it cool slightly before mixing with brown sugar, white sugar, pure vanilla extract, and a large egg in another bowl.

In a medium bowl, whisk together all-purpose flour, baking powder, baking soda, and salt. Gradually combine the dry ingredients with the wet mixture. Fold in semisweet chocolate chips, chopped Oreo pieces, and Oreo crumbs until just combined.

In another microwave-safe bowl, melt a semi-sweet chocolate bar for about 1 minute, stirring until smooth. Allow to cool, then beat unsalted butter with both sugars until light and fluffy.

Add the melted chocolate and pure vanilla extract, mixing until incorporated. In a separate bowl, whisk together flour, cocoa powder, baking powder, and salt; gradually add to the chocolate mixture along with an egg.

Finally, add chocolate chips, Oreo pieces, and crumbs.

Chill the brownie cookie dough in the refrigerator for about 10-15 minutes. Use the Oreo chocolate chip cookie dough immediately.

Drop rounded tablespoons of both doughs onto a lined baking sheet, flatten slightly and swirl together, then roll into balls.

Preheat oven to 350°F (175°C). Bake the cookies for 13-15 minutes, checking for golden edges and slightly underbaked centers.

Remove from the oven, sprinkle with extra Oreo chunks and chocolate chips. Cool for 5 minutes on the sheet, then transfer to a wire rack.

Enjoy warm or at room temperature.