Good stuff! You could probably use Baileys or whatever else you like to flavour this. Start with the tablespoon of rum and see how it goes. You can add more if you NEED to.
1 cup storebought chocolate milk
1 tablespoon unsweetened cocoa
1 teaspoon brown sugar
1 tablespoon (or more!) white rum
In a small pot, heat up the chocolate milk over medium heat until it's steaming. Whisk in the other ingredients. Serve hot with whipped cream or marshmallows.