1 cup butter
1 (1-pound) package brown sugar (2-1/4 cups packed)
1 (14-ounce) can sweetened condensed milk
1 cup light corn syrup
1 tsp vanilla
Recipe
Line a 9x9x2-inch baking pan with foil, extending foil over edges of pan. Generously butter foil; set pan aside. In a heavy 3-quart saucepan, melt 1 cup butter over low heat. Add brown sugar, sweetened condensed milk, and corn syrup; mix well. Carefully clip candy thermometer to side of pan. Cook over medium heat, stirring frequently, until thermometer registers 248°, firm-ball stage. Mixture should boil at a moderate, steady rate over entire surface. Reaching firm-ball stage should take 15 to 20 minutes.
Remove saucepan from heat; remove candy thermometer from saucepan. Immediately stir in vanilla. Quickly pour caramel mixture into prepared baking pan.
When caramel is firm, use foil to lift it out of pan. Use a buttered knife to cut candy into 1-inch squares. Wrap each piece in clear plastic wrap.