Prepare the brownies according to the package directions with the addition of the chocolate chips.
When the brownies are done, leave the oven on and let them cool. Sprinkle the marshmallows over the top of the warm brownies, cover marshmallows with graham cracker crumbs and a sprinkling of chocolate chips. Put the brownies back in the oven for a minute, or until marshmallows puff up. You can also broil the brownies for 30 seconds.
Let brownies cool completely and then cut with a sharp knife coated in cooking spray. You will have to put cooking spray on the knife several times but this keeps it from sticking to the marshmallows