In a medium pot, combine the chocolates, cocoa powder, salt, sugar and milk and set over medium-low heat, stirring often (a whisk is helpful here) so the cocoa doesn't stick to the bottom. Bring it to just before the boil, stirring often. Remove from the heat, add the Fernet Branca and Angostura. Serve hot with, if you like, marshmallows and a little grated fresh cinnamon on top.