It is important to use whole or two percent milk in this recipe for a rich and creamy froth.Plus: Ultimate Cocktail Guide
In a heavy, medium saucepan, bring the sugar and water to a boil. Cook over moderate heat, without stirring, until a deep amber caramel forms, about 12 minutes. Remove the pan from the heat. Slowly and carefully add a little of the cream to stop the cooking, then whisk in the remaining cream until the sauce is smooth. Let cool to room temperature.
In a large saucepan, simmer the milk with the vanilla bean over moderately low heat for 5 minutes. Remove from the heat and stir in the coffee liqueur. Remove the vanilla bean and scrape the seeds into the milk. Using an immersion blender, beat the milk until a layer of froth forms. Pour off the milk into warm mugs, then spoon the froth on top and drizzle with the caramel sauce. Serve at once.
The caramel sauce can be refrigerated for up to 1 week; reheat before using.