In a mug, combine the coconut milk, cocoa powder, sugar, salt, and cinnamon (if desired).
Add boiling water and stir until powder is dissolved. To make the hot chocolate frothy, use a milk frother or pour into a blender and blend for a few seconds to desired frothiness. Top with marshmallows.
To make hot chocolate mix:
In a pint-sized canning jar, combine 6 tablespoons powdered coconut milk, 2 tablespoons cocoa powder, 2 tablespoons plus 2 teaspoons granulated sugar, 2 tablespoons cocoa powder, ¼ teaspoon salt, and ¼ teaspoon cinnamon (optional). Cover the jar and shake well to evenly distribute the ingredients. Fill the remaining space in the jar with mini marshmallows (optional).