Coarsely crush the spices and put them with the butter and brown sugar in a small saucepan. Melt over low heat, mix well until sugar has dissolved.
Leave to infuse for 2 minutes, and then filter through a sieve into a clean container.
When mixture is cool, store in the fridge.
In each mug, place 1 teaspoon of cold spiced butter, 40 millilitres of rum, and then top with boiling water.
For an extra touch of indulgence, serve topped with a sprinkle of Ground Cinnamon.