Line bottom and sides of an 8-inch square baking pan with parchment paper and oil parchment.
Bring brown sugar, cream, butter, salt, and ½ cup rum to a boil in a 3- to 4-quart heavy saucepan, stirring until butter is melted, then boil over moderate heat, stirring frequently, until thermometer registers 248°F (firm-ball stage), about 15 minutes.
Remove from heat and stir in vanilla and remaining teaspoon rum. Pour into baking pan and cool completely until firm.
Cut into 1-inch squares. You can wrap each piece in wax paper or stack in a tin, making sure to put wax paper between the layers.
Recipe by I'm At Home Baking! at http://imathomebaking.com/butter-rum-caramels/