Grate or break up chocolate. Combine all ingredients in heavy medium saucepan. Stir over low heat until chocolate melts. Increase heat and bring just to a boil, stirring often. Remove from heat and whisk until frothy. Return to heat and bring to boil again. Remove from heat, whisk until frothy. Repeat heating and whisking once again. Discard orange peel. (Can be prepared 2 hours ahead. Let stand at room temperature. Before serving, bring just to boil, remove from heat and whisk until frothy.) Pour hot chocolate into coffee mugs. Makes 2 servings.
Serve in a Collins Glass