Pre heat the oven to 180C for 20 minutes.
Grease and line a 8X8 square pan with parchment paper. Keep aside.
For the cookie dough - In a large bowl, cream together the butter and sugars with a hand mixer. Add the eggs one at a time and beat well, scraping down the sides of the mixing bowl as you beat. Add the flour, salt, baking soda and baking powder and mix on low until incorporated. Fold in the chocolate chips.
Gently pressing the cookie dough into the bottom of the lined pan, making sure to spread it in an even layer. My layer came to be pretty thin and that is how I like it.
On top of this spread the whole oreo cookies (tip : our sunfeast dark magic works brilliantly well as well, infact works better) as close to each other as possible. Set aside.
For the brownie batter - In a large microwave friendly mixing bowl, melt the butter. Once melted, add the sugar and cocoa powder. Stir to incorporate. Put it back in the microwave for 10 seconds if the mixture feels too stiff. Add the salt, vanilla and eggs to the batter and then whisk until combined. In a separate bowl, sift the flour and then slowly incorporate the flour into the batter until it's all mixed.
Pour the batter on top of the prepared pan with cookies.
Bake in a pre heated oven at 180 C for 30-35 minutes. Don't over cook.