Melt the butter in a saucepan or in the microwave in a microwave-safe bowl. Mix in the sugar, eggs and vanilla. Then, mix in the cocoa powder, all-purpose flour, salt, and baking powder. Fold in the chocolate chips. Pour 1/3 of the batter into the pan, and then place about 16 Oreos into the batter, pressing down as much as possible. Spread the remaining batter on top. Use a spoon to try to spread the batter over the Oreos as much as possible.