Chop the chocolate bar into small pieces.
In a medium saucepan, heat the milk over medium-low heat.
Add the chocolate, sugar, cinnamon, vanilla, cayenne pepper, and sea salt. Bring to a gentle simmer, whisking regularly, being sure not to let the milk boil.
Simmer until the chocolate is completely melted and the mixture is hot, about 10-15 minutes.
Pour hot chocolate into mugs and top with whipped cream, red pepper flakes, and cinnamon sticks.