01 - In a small saucepan over medium heat, combine milk, chopped dark chocolate, cocoa powder, sugar, cinnamon, nutmeg, optional cayenne, and salt.
02 - Whisk continuously until the chocolate fully melts and mixture is smooth and steaming, approximately 5 to 7 minutes, avoiding boiling.
03 - Remove saucepan from heat and stir in pure vanilla extract.
04 - While the base warms, whip heavy cream, powdered sugar, and vanilla extract in a chilled bowl until soft peaks form.
05 - Pour hot chocolate into mugs.
06 - Generously top each serving with whipped cream.
07 - Optionally garnish with a dusting of ground cinnamon or chocolate shavings, then serve immediately.