Pour the milk into a saucepan and bring it almost to the boil. Remove the pan from the heat and tip in the chocolate. Leave to stand for 2–3 minutes, stirring frequently, until the chocolate has melted.
Add the vanilla extract to the saucepan. Beat with a balloon whisk or an immersion blender until the milk is smooth and topped with a thick foam.
Pour the hot milk between 2 mugs and serve sprinkled with cocoa. Decorate with a vanilla pod, if liked.