Get a good mug. Add 2 oz. dark rum, 1 tsp demerara sugar, and 3-4 oz. water. Take a metal poker, and heat it in the fire until white-hot. Plunge it into the mug until the hissing stops.
Add a little! pat of butter, and a pinch of nutmeg.

Or you can rinse a mug with boiling water, add the rum, sugar and boiling water, then top with butter and nutmeg.

Thanks, Esquire!