Finely rub about 1 tablespoon of the chocolate for the garnish and set aside. Use a knife to cut or chop the remaining chocolate into large pieces. Heat the cream, but do not bring it to a boil. Dissolve the chocolate in the cream while stirring, season with cinnamon and cardamom. Stir in the coffee and pour the mixture into preheated glasses. Add sugar to taste. Warm up the milk, whip until frothy and pour onto the coffee. Garnish with the grated chocolate.
Tip: UHT milk is best for whipping until frothy (H = homogenized)