Hot Buttered Rum
1 teaspoon butter
2 teaspoons brown sugar
5 ounces boiling water
2 ounces rum
Garnish: Freshly grated nutmeg and optionally a stick of cinnamon.
Put the butter and sugar into a pre-heated mug and add the boiling water. Stir to dissolve, then add the rum and stir again.

For some reason, people have gotten into the habit of thinking that in order to make a Hot Buttered Rum, you need to use a batter mix. This means either taking the time to mix it up from scratch yourself, or buying a pre-mix from the store. Either way, you will end up with far too much if all you want is a single drink. There isn't any reason why you can't mix up a Hot Buttered Rum ala minute, so why not?