Prepare brownie batter according to package directions. Spray the appropriate sized baking dish with cooking spray and pour batter into prepared pan.

Bake according to package directions.

Turn oven to broil if your baking dish can handle higher temperatures. If not, keep the oven set to the temperature you baked the brownies in.

Place the marshmallows on top of the brownies.

Place the marshmallow-topped brownies into the oven, watch carefully and remove when the marshmallows are melted and beginning to turn a golden brown color, about 2-4 minutes.

Drizzle hot fudge sauce over top of toasted marshmallows.

Crumble half of the graham crackers and scatter over the melted marshmallows.

Break the remaining graham crackers and insert them randomly into the toasted marshmallows.

Serve immediately.