Preheat oven to 350°F. Grease a 8x8" pan and line with parchment paper, if desired. Set aside.
In a medium microwave-safe bowl, add the butter and peanut butter. Microwave in 30 second intervals until the butter is completely melted.
Add in the granulated sugar, light brown sugar, egg, egg yolk, and vanilla extract. Whisk together until everything is combined.
Add the flour, baking powder, and salt to the bowl. Mix until the batter forms. Lastly, fold in the chopped Oreo cookie pieces.
Spread the blondie batter evenly in the prepared pan. Top with more Oreo chunks, if desired. Bake for 30-34 minutes. The center will still be slightly soft, but the edges will just be starting to brown. Allow the blondies to cool completely before slicing. Enjoy!