In a small saucepan bring half-and-half, butter and 1 tablespoon of the rum to simmering. Remove from heat; whisk in chocolate until melted. Whisk in the remaining 1 Tbsp. of rum (if necessary add an additional tablespoon half-and-half to make dipping consistency). Transfer the chocolate mixture to a small fondue pot or a 10-ounce custard cup. Serve with dippers.