Spread a thin layer of marshmallow fluff around the rim of your cup using the back of a spoon. Crush the graham cracker in a Ziploc bag with a rolling pin until fine and then add to a plate. Roll the rim of the cup in the crumbs until coated.
Drizzle chocolate sauce into the bottom of a cup. Brew two shots of espresso and pour them over the sauce, stirring to dissolve. Add milk and ice to fill the cup. Set aside.
In a separate cup, combine the toasted marshmallow syrup, milk, and heavy cream. Froth with a handheld frother until thick and fluffy (about 15 seconds).
Pour the cold foam over the iced latte, and finish with a drizzle of chocolate sauce on top.