Heat the butter in a small saucepan until it is runny but not hot. Mix the sugar, nutmeg, cinnamon, cardamom and clove in the butter and let everything cool. Possibly put in a sealable container for portioning and cool.
Now put about the amount of a tablespoon of this mixture per serving in a mug or a grog glass. Pour 4 cl rum over it and fill up with hot water. Stir briefly and serve.