In a small saucepan over medium heat, warm the milk until steaming but not boiling.
Whisk in the cocoa powder, honey, cinnamon, and chopped dark chocolate. Continue whisking until the chocolate is fully melted and the mixture is smooth.
Let the hot chocolate heat for another 2–3 minutes, stirring occasionally, until warmed through and slightly thickened.
Remove from heat and pour into mugs. Serve immediately, topped with whipped cream, frothed milk, or a light sprinkle of cinnamon or cocoa powder if desired.