For each cup, combine first three ingredients in a double boiler, and stir until completely melted.

Whisk in half-and-half after chocolate/butter/vanilla mixture has melted. Continue heating. Do not boil.

Serve over miniature marshmallows (optional) and garnish with a dash of nutmeg

For variation, substitute dark (semisweet) chocolate or white chocolate. Also try adding liqueurs - Kahlua (milk chocolate), Contreau (dark chocolate), peppermint schnapps (white chocolate).