01 - Combine milk and heavy cream in a medium saucepan over medium-low heat. Heat gently until steaming, avoiding boiling.
02 - Add chopped chocolate, cocoa powder, sugar, and salt to the warm dairy. Whisk constantly until chocolate is completely melted and mixture is smooth and creamy, about 3 to 5 minutes.
03 - Remove from heat and stir in vanilla extract. Adjust sweetness by tasting and adding sugar if desired.
04 - Ladle into mugs and garnish with whipped cream, chocolate shavings, or marshmallows as preferred. Serve immediately.