Melt butter over medium heat in a medium sized saucepan.
Stir in the brown sugar and heat until sugar is dissolved.
Add the cinnamon, nutmeg and sea salt, stir to combine. Continue to heat and stir for 2 to 3 minutes.
Whisk in the water and bring up to a simmer.
Once heated through, remove from heat and stir in the rum. Divide the mixture between two mugs, garnish with freshly grated nutmeg (if desired) and serve.
Notes
Substitute any type of alcohol that you like.
Adjust spices according to tastes - add cloves or allspice if desired.