Preheat your oven to 350°F (175°C).
In a double boiler or microwave-safe bowl, combine the chopped unsweetened baking chocolate and sliced butter. Heat until melted and smooth.
In a large mixing bowl, combine the granulated sugar and unsweetened cocoa powder. Stir until well blended.
Pour the melted chocolate and butter mixture over the sugar and cocoa. Stir until fully combined.
Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract.
Sprinkle the salt and all-purpose flour over the wet mixture. Gently fold the ingredients until just combined.
Chop the Oreo cookies into quarters and gently fold them into the brownie batter.
Pour the brownie batter into a greased 8x8 inch baking pan and bake for 30-35 minutes.
Let the brownies cool in the pan for about 10 minutes, then transfer to a cooling rack to cool completely before cutting.
