Mix 1 cup water with masa harina. Let stand 15 minutes. Bring remaining 1 1/2 cups water to boil in heavy medium saucepan. Strain masa harina mixture into boiling water. Add chocolate and stir until melted and smooth. Add cinnamon stick. Stir over low heat until mixture thickens or whip to frothy consistency with a molinillo, about 5 minutes. Stir in brown sugar.
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