Heat the water in an electric kettle (or regular stovetop kettle or saucepan) until it starts to bubble. (See Notes)
Meanwhile, gather your garnishes (lemon slice, cinnamon stick and star anise) and have them ready to go.
Add the dark rum, lemon juice and honey to your serving mug.
When the water boils, pour it into your serving mug.
Use the cinnamon stick or a spoon to stir the cocktail. The honey should all dissolve after the hot water is added.
Add all of the garnishes, and serve.
Notes
You don't need to bring the water all the way to boiling for this cocktail, just until it starts to steam or simmer. Alcohol starts to evaporate at 172°F (78°C), so if you have the water much hotter than that, it's going to be too hot for the rum to handle! You can use a kitchen thermometer if you want to be exact.