1. Preheat the oven to 350 degrees fahrenheit.

2. Start by making the graham cracker crust by pulsing the graham crackers and brown sugar together in a mixer until they are a crumb consistency.

3. In a medium mixing bowl, add the graham cracker mixture to the melted butter and mix together until coated.

4. Line the pan with parchment paper to prevent the brownies from sticking.

5. Mold the graham cracker crust into the bottom of the pan until evenly spread. Bake in the oven for 15 minutes, then remove from the oven and set aside.

6. While the crust is baking, brown the butter for the brownie batter in a small pot. Stir continuously until the melted butter begins to create brown bits at the bottom of the pot and give off a nutty scent. 

7. Add the chopped semi sweet chocolate immediately to the hot butter and mix together until completely melted. Remove from the heat.

8. In a separate bowl, combine the sugar, brown sugar, eggs and vanilla. Beat until thick and fluffy, using a stand mixer or hand mixer.

9. Pour in the brown butter and melted chocolate mixture and mix together on low speed until combined.

10. Fold in the cocoa powder and espresso powder until combined.

11. Pour the brownie batter into the pan over the graham cracker crust and spread evenly. 

12. Bake for another 35-40 minutes. The brownies should look set and no longer jiggle when you pull them out of the oven.

13. Turn your oven on low broil. 

14. Pour the mini marshmallows evenly on top of the brownies.

15. Place back in the oven for another 3-5 minutes, watching closely until the marshmallows have toasted and reached a golden brown color.

16. Remove from the oven and let the brownies rest for 30 minutes at room temperature.

17. Cut the brownie into bars, serve and enjoy!