Pour the almond milk, cacao, syrup, and cinnamon into a medium sized pot over medium high heat. Stir until all lumps are removed.
Allow the mixture to come to a low boil (about 5 minutes), then reduce the heat.
Add the rum (optional). Stir well and remove the mixture from the heat.
Pour the hot chocolate into your favorite mug. Top with marshmallows and cinnamon.