Soften the butter ahead of time — leave it at room temperature for 10–15 minutes or nuke for 5–7 seconds if you’re in a rush (don’t melt it).

Measure your rum, brown sugar, and spices so they’re within arm’s reach.

Warm the mug by filling it with hot tap water for a minute, then dump it out — a warm mug keeps the drink hotter longer.

In a small bowl, add 1 tablespoon softened unsalted butter, 1 tablespoon brown sugar, and the pinches of cinnamon, nutmeg, and cloves.

Use a fork or small whisk to mash and blend until the mixture is glossy and mostly lump-free — it should look like a thick, spreadable paste.

If the butter feels too firm, soften it a touch more; if it’s too wet, add a tiny pinch more brown sugar.

Pro tip: For the smoothest texture, press the mixture through the tines of a fork while whisking — this helps break up any tiny lumps and makes the paste emulsify into the hot liquid more easily.

Pour about ½ cup of water (or hot apple cider for a richer twist) into a small saucepan.

Warm it until steaming and just below a simmer; you want it hot enough to melt and dissolve the paste, but avoid a rolling boil.

Pro tip: Don’t boil the liquid — boiling drives off aromatics and can make the drink taste flat. Steaming/just-off-the-boil is perfect for hot rum drinks.

Spoon the spiced butter paste into your warmed mug.

Pour in 2 ounces of dark or spiced rum over the paste. (If you’re aiming for a more aromatic spiced rum cocktail, use spiced rum here.)

Slowly pour the hot water (or cider) into the mug.

Stir vigorously with a long spoon or whisk for 20–30 seconds until the butter paste fully melts and the drink looks silky and slightly glossy.

Pro tip: Whisk continuously when you first combine the butter paste and hot liquid — this prevents lumps and helps the butter emulsify into a velvety texture.

Taste the drink and tweak: add a little extra brown sugar for sweetness, another tiny pinch of cinnamon for warmth, or a splash of heavy cream for extra richness.

Garnish options: a dollop of whipped cream, a cinnamon stick for stirring, or a light grating of fresh nutmeg on top. A thin lemon twist is a nice, unexpected bright note if you like a bit of contrast.

Pro tip: If you top with whipped cream, spoon it gently so the heat doesn’t immediately melt it away — it creates a lovely creamy layer to sip through.

To serve a crowd, make a larger batch of the spiced butter paste (multiply the recipe), keep it chilled in a jar, and set up a station with warmed water/cider and measured rum. Guests can assemble to taste.

Leftover butter paste keeps in the fridge for up to two weeks — scoop a tablespoon into mugs as needed for instant hot buttered rum.