Take a clear tempered (heat-proof) glass with a volume of at least 5 ounces (a Duralex Picardie tumbler is perfect, although a small coffee mug will serve). Heat the glass by filling with hot water. Wait 30 seconds, then drain and dry the glass.

Add the sugar, whiskey, and coffee to the warmed glass. Stir to dissolve the sugar, about 10 seconds. Slowly pour the whipped cream over the back of a spoon so it lands gently—it should float on the whiskey-and-coffee mixture. Add enough whipped cream to measure about ½ inch in the glass. Sprinkle with the optional nutmeg if using, and serve immediately.