Spread crushed graham cracker in a circle on a small plate.
Apply ¼ teaspoon of the chocolate syrup to a paper towel and run it along the rim of a latte mug to coat, then dip the rim in the graham cracker crumbs.
Drizzle the remaining chocolate syrup inside the mug.
In a large mug steam cold milk using the steaming/frothing wand with the frothing part removed. Heat until 145-160 degrees Fahrenheit, then set aside.
Brew the espresso according to manufacturer’s directions and pour over the chocolate syrup.
Pour the steamed milk into the mug, then spray a little whipped cream on top of that.
Sprinkle 1-2 teaspoons of remaining graham cracker crumbs and the mini marshmallows over the whipped cream.