1/2 cup firmly packed brown sugar
1/3 cup dark rum
1/2 cup unsalted butter, softened
1/4 teaspoon kosher salt
In a small skillet, bring brown sugar and rum to a boil over medium-high heat, stirring until sugar dissolves. Stir in butter until melted. Simmer until sauce becomes thick and syrupy, about 5 minutes. Stir in salt; remove from heat. Let cool slightly before using.
makes 3/4 cup