In a thick bottom pan, bring milk to boil, add the chopped dark chocolate and stir to melt.
When the chocolate is completely melted, add the honey sugar and cinnamon stick.
Heat gently, and keep stirring constantly. When the drink becomes little more thick, add the vanilla and rum if you are adding at this stage.
You can switch off when little bubbles form all the way around the sides of the pan.
Allow to cool a bit, remove the cinnamon stick, pour into serving mugs and serve.