In a small saucepan, heat the milk and heavy cream over medium heat, stirring occasionally until it begins to steam.
Add the dark chocolate to the saucepan and stir until completely melted and smooth.
Taste the mixture and add sugar if desired. Stir until dissolved.
Remove the saucepan from heat and stir in the vanilla extract.
Pour the hot chocolate into mugs, and top with whipped cream.
Dust the whipped cream with cocoa powder for an extra touch of indulgence.