Heat milk with chocolate over medium heat, periodically stirring with a whisk until a homogeneous chocolate mass. Do not boil.
Remove milk from heat, add cinnamon, mix. Put the banana in a blender, pour chocolate milk with cinnamon on top. Beat until smooth for about 30 seconds.
Try a drink, if the banana was not very ripe, add 1-2 tablespoons of sugar. Pour the chocolate into cups. Serve hot.