My Dad would sometimes make hot buttered rum after winter sports.
He would boil water, add a healthy splash of rum, add a teaspoon of brown sugar, stir, grate on some nutmeg and a jot of butter on top. He would make it for the kids with apple juice instead of the rum.
Use a high-quality rum such as Appleton’s or Mount Gay. Your ratio of rum to water is one-part alcohol to six parts hot water.