In a large bowl, whisk together the butter and sugars until combined.
Add the egg and vanilla and whisk vigorously for a few minutes until thickened. You want to beat the egg more than you would normally to help create a glossy and crackly top.
In a small bowl, whisk together the dry ingredients (cocoa powder, flour, espresso powder, baking powder, salt).
Add the dry ingredients into the wet mixture and stir to combine.
Once your batter is formed, stir in the chocolate chips.
Pour the batter over the oreo layer and use a rubber spatula to smooth out the brownie layer.
Bake for 35-40 minutes, until the center is set and a toothpick inserted into the center comes out almost entirely clean.
Allow the brownies to cool in the pan for an hour before transfering to a cooling rack. To transfer, run a knife around the edge of the pan and then simply lift the parchment paper out of the baking dish.
Allow to cool on the cooling rack for at least another until, until room temperature. It is so hard to cut these when they are still warm.
If you are so inclined, you can melt an additional tablespoon of peanut butter in the microwave and drizzle that over top of the brownies. Not necessary but extra peanut butter is always extra delicious!
Slice and enjoy!