Prepare a shot of espresso.
Heat the milk until steamed and frothy (optional). If you don't have an espresso machine or prefer not to use one, brewed coffee may be used as well. For non-dairy options, consider using almond or soy milk instead.
In a large mug, combine the shot of espresso/brewed coffee with hot water and chocolate syrup (or mix cocoa powder in steamed milk). Stir well to ensure ingredients are fully integrated. Add vanilla extract for flavoring if using.
Pour the steamed milk over the mug, filling it nearly up to the top without mixing them together immediately – let sit for a few seconds so they naturally combine as you stir gently and create layers in your drink (optional). Then slowly mix everything until well combined. Add more chocolate syrup or whipped cream on top if desired.