In a small pot, bring half and half to a boil. Remove from heat and add to chocolate in a bowl. Stir until chocolate has fully melted.
Return chocolate liquid to the pot, or refrigerate until ready for use.
Before serving, add milk. Warm over medium heat, stirring occasionally until it simmers.
Pour into individual mugs. Stir in 1 ounce of creme de menthe to each mug just before serving.
Recipe courtesy of Bob Blumer, Surreal Gourmet