Preheat oven to 375. Line an 8x8 inch pan with foil and spray with cooking spray, set aside.
In a medium sauce pan, melt butter of medium heat. Stir in cocoa powder and vanilla.
Pour mixture into a large mixing bowl. Add eggs, sugars, and flour and mix until all ingredients are incorporated and well combined.
Pour half of batter into prepared pan. Lay a single layer of oreos side by side on top of batter. Pour remaining batter over oreos and spread evenly. Bake 30-40 minutes until a toothpick comes out mostly clean.
Melt chocolate chips, then spread over brownies. Sprinkle with optional sugar if desired. Allow to cool completely before cutting into squares.