Stir together 2 cups milk, chopped Mexican chocolate, and vanilla extract in a saucepan over low heat until chocolate melts and mixture is smooth. Cook, whisking constantly, just until mixture is thoroughly heated.
Remove from heat, and whisk mixture until foamy. (An immersion blender also works well.)
Pour evenly into 2 mugs; top with whipped cream, and add a cinnamon stick, if desired.
