In a small saucepan, combine cocoa powder, brown sugar, and coffee.
Pour milk and cream over the cocoa powder mixture. Stir until well combined for 5 minutes.
Over the stovetop to very low heat and continue to stir until the hot chocolate mixture starts to heat up without allowing it to simmer or boil, about 3 to 5 minutes.
Add chopped chocolates. Continue stirring for 2 minutes or until the chocolates are completely melted. Turn off the heat. Cool for 1 minute and transfer hot chocolate to a serving glass.
Top with mini marshmallows and dust with cocoa powder.
Notes
Heat should be very low at 140°F (60°C).Continue stirring to avoid milk and cream from curdling.Unsweetened cocoa powder is used to deepen the chocolate flavor.Coffee is added to heighten the chocolate flavor. I use extra strong instant coffee.This is a very large serving and can easily be enjoyed by two.