PLACE coffee and chocolate in heavy saucepan; cook on very low heat until chocolate is melted and mixture is well blended, stirring constantly with wire whisk.
STIR in sugar and cinnamon. Bring to boil on medium heat; cook until sugar is dissolved, stirring constantly. Gradually add milk and vanilla, stirring until well blended. Cook until heated through, stirring occasionally.
POUR into 4 large cups or mugs. Top with whipped topping. Garnish with a light sprinkling of additional cinnamon, if desired.