In a medium saucepan over medium heat bring soy milk, cinnamon sticks, and ginger slices to a simmer (if using vanilla bean, split the bean open and add here as well), until you see small bubbles appear, about 5 minutes. Do not allow the mixture to boil.
Once the mixture simmers for a few minutes to allow the ginger and cinnamon to infuse into the milk, remove from heat and strain the milk from the cinnamon and ginger then return the milk to the pot.
Over low heat, add the cocoa powder, vanilla extract or paste, sugar, and a pinch of sea salt and stir with a metal whisk until the cocoa powder has completely dissolved.
Add the dark chocolate pieces and stir until completely dissolved about 1 minute. Simmer for an additional minute to thicken the chocolate. Serve immediately and top with marshmallows or non-dairy whipped cream, and a dusting of more cocoa if desired.
Notes
This French hot chocolate is thick and decadent in consistency but not very sweet which is how it is served in France. If you prefer a sweeter American-style hot chocolate, add more sugar to your taste.