In a small saucepan, whisk water and cacao powder until smooth. Add cinnamon and a pinch of salt.
Warm over medium heat, whisking to break up any lumps.
Don’t let it boil—just steam.
Pour in the milk and keep whisking until hot and slightly frothy, 2–3 minutes.
Remove from heat. Stir in vanilla and your sweetener. Taste and adjust cinnamon or sweetness.
If using coffee or espresso, stir it in now for a bolder, mocha-style latte.
Pour into a mug.
Garnish with a light dusting of cinnamon or a few cacao nibs, if you like. Enjoy warm.