Add the chopped chocolate, cocoa powder, sugar, salt, and eggnog to a small saucepan.
Set the mixture over medium heat, stirring often until the chocolate has melted and fully combined with the mixture.
Bring the mixture to a simmer, then pour between two glasses. Top with marshmallows, then serve and enjoy!
Notes
If you'd like to do the garnish I did in the photos, simply use the back of a spoon to swirl marshmallow fluff on the inside of your glass before pouring in the hot chocolate!