Old-Time Fudge
["2 sq. (2 oz.) unsweetened chocolate, cut up", "2 c. sugar", "3/4 c. milk", "1 tsp. light corn syrup", "2 Tbsp. margarine", "1 tsp. vanilla", "1/2 c. coarsely chopped nuts"]
["Line a 10-inch square pan with foil; extend foil over edges of pan.", "Butter foil; set aside."]
["chocolate", "sugar", "milk", "light corn syrup", "margarine", "vanilla", "nuts"]