Step 1: Preheat the oven to 175 degrees C. Grease a 8 inch square baking tin.
Step 2: Start by taking 2/3 of the oreos and bashing into medium sized chunks, put to one side. In a large saucepan, melt the butter. Remove from the heat and stir in sugar, eggs and vanilla extract. Beat in cocoa powder, flour, salt and baking powder until smooth (make sure there are no lumps!). Add the crushed oreos and stir in. Pour into the tin, then take the remainder of the oreos and break roughly in your hands and sprinkle on the top. Place the tin into the oven and cook for 25-30 minutes, or until a knife can be inserted and comes out clean.
Step 3: This is great served on its own, with custard, or ice cream!