1 (1.55 ounce) bar milk chocolate candy bar, chopped
2/3 cup milk, or more to taste
1 pinch ground cinnamon (optional)
Place chocolate pieces in a saucepan over medium-low heat; add milk and whisk constantly until chocolate is melted and well blended, about 5 minutes. Whisk in cinnamon. Remove from heat; add more milk if desired. Serve in a mug.