In a heavy saucepan, heat the milk, ground cinnamon and cinnamon stick until simmering. Add the chocolate and let melt. Remove from heat and add vanilla extract. Transfer to mugs and serve with whipped cream.
Courtesy Gale Gand, "Butter Sugar Flour Eggs" by Gale Gand, Rick Tramonto, Julia Moskin, Clarkson N. Potter Publishers, 1999