Place the marshmallows into a glass or mug large enough to hold the milk with a bit of extra space.
Heat the milk until it’s almost boiling.
Pour the hot milk over the marshmallows and use a hand frother to combine and froth the mixture.
In a separate mug, stir together the hot espresso and melted chocolate until smooth.
Pour the frothed marshmallow milk over the coffee and chocolate mixture.
Sprinkle graham cracker crumbs on top.
Toast 2–3 large marshmallows on a small skewer until golden brown.
Place the skewer over the top of the prepared coffee as an additional garnish.