Hot Buttered Rum

Combine ½ stick (¼ cup) unsalted butter, ¼ cup packed dark brown sugar, 1 tsp. cinnamon, ½ tsp. freshly grated nutmeg, ¼ tsp. ground cloves, ⅛ tsp. kosher salt, and 2 cups water in a 1½–2-qt. saucepan. Place over medium-high heat and bring just to a boil; reduce heat and simmer, whisking occasionally, about 10 minutes until fragrant and slightly reduced. Remove from heat and stir in ⅔ cup aged dark rum. Serve hot.