Tip
To pour a hot liquid into a glass, first place a spoon in the glass then pour the liquid over the spoon in order to prevent the glass from cracking.

1. Gently heat the milk over moderate heat with the vanilla bean and sugar, without letting it boil; once it is hot, reduce the heat to minimum and infuse for 10 minutes; scrape the seeds from the vanilla bean;
2. pour the hot coffee and grated chocolate into the hot milk; increase the heat to medium until the chocolate is melted; whisk until foamy; 
3. pour into glasses; garnish with whipped cream and serve immediately. You can serve it with a cinnamon stick to stir the cream into the mocha.