01 - Combine milk and heavy cream in a medium saucepan. Warm gently over medium heat until steaming, avoiding boiling.
02 - Whisk in the chopped dark chocolate and cocoa powder until fully melted and the mixture is smooth.
03 - Add sugar, cinnamon, nutmeg, cayenne pepper if using, vanilla extract, and salt. Whisk continuously until mixture is hot and ingredients are well blended.
04 - Taste and modify sweetness or spice level as preferred.
05 - Pour into mugs and garnish with whipped cream, chocolate shavings, or a cinnamon stick if desired. Serve immediately.