Preheat oven to 350°F and line a 8x8 square pan with parchment and set aside.
In a bowl whisk flour, cocoa powder, salt and espresso powder (if using), set aside.
Take the butter and ½ cup of chocolate chips and melt in microwave until just melted making sure to stir in between.
With mixer and paddle attachment mix the sugars and melted chocolate mixture together for about 3 mins.
Add eggs and vanilla and mix.
With mixer on low add dry ingredients and mix until just combined.
Now take your Oreos and ½ cup of chocolate chips and fold into batter. Pour into 8x8 pan and top with remaining chocolate chips and extra Oreos pieces.
Bake for 25-30 depending on how you like them done. I take them out at 25 mins. for more fudgy center, they do continue to bake from residual heat of pan while cooling.
Cool in pan for 20 mins before transferring to cooling rack to cool completely.