Add the graham crackers to a food processor (or add them in a ziplock bag and smash with a rolling pin) and process until fine crumbs.

Slowly add in the melted butter while processing. Crumbs should stick together when pressed, if not, add more butter.

Spray a 9x13 pan with non-stick spray, and press the crumbs into the bottom to create a crust.

bake for 5-7 minutes in 350* oven, or freeze for 10 minutes for crumbs to set.

Meanwhile, prepare brownie batter according to package instructions.

Pour batter over crumbs (once the crumbs have set) and bake in 350* oven until brownies are set. (follow the directions on brownie box for time)

Once brownies are fully baked, pour the marshmallows on top and create a nice even layer. Put under the broil for about 30-60 seconds or until marshmallows are golden brown and melting.

Let brownies totally cool before cutting.