Combine Chocolate Syrup and Vanilla: In a mug, combine the chocolate syrup and vanilla extract.
Add Coffee: Pour the espresso or strong brewed coffee into the mug. Stir to combine.
Heat the Milk: Heat the milk in a saucepan or microwave until warm. You can froth it with a milk frother if you like for extra creaminess.
Pour the Milk: Pour the warm milk into the mug. Stir gently.
Top with Marshmallows: Place the toasted marshmallows on top of the mocha.
Add Optional Toppings: Garnish with whipped cream, chocolate shavings, extra marshmallows, or graham cracker crumbs, if desired.