Grease a 7×7-inch baking pan with butter & line with parchment paper
Preheat the oven at180c for 15minutes
In a heat resistant bowl add dark chocolate & butter. Melt in a microwave 20sec interval or over a double boiler.Mix and melt completely. cool down completely.set aside
In a different bowl add both sugars,eggs & vanilla and whisk well until creamy
Add chocolate & butter mixture to it and mix again for 1-2min
Add sifted flour, cocoa powder and salt.Fold using a spatula
Now pour the half batter into the prepared baking pan, add chocolate chips & pour the remaining batter
Bake for 30-35min (depends on the oven, don't over bake)
Remove from the oven and let it cool for 30min
Remove from the baking pan & let it cool completely for 1-2 hr
Slice them into 9 square using a sharp knife