Combine the first 4 ingredients in a large Dutch oven; cook over medium heat until thoroughly heated. Place chocolate morsels in a medium bowl. Microwave at high, uncovered, 1 minute 30 seconds; stir until smooth. Gradually add 1 cup hot milk mixture to melted chocolate, stirring with a wire whisk until smooth. Add chocolate mixture to remaining milk mixture. Stir in coffee. Add Kahlua, if desired. Cook over medium heat until steaming but not boiling. Serve warm with whipped cream.