In a 3 1/2- to 4-quart slow cooker, combine milk, chocolate pieces, coffee powder, and 1 teaspoon cinnamon.
Cover; cook on low-heat setting for 4 hours, whisking vigorously once halfway through cooking time. Whisk well before serving. If desired, sprinkle each serving with cinnamon.
1 fat, 1/2 other carbohydrate, 1/2 milk