Cook sugar, milk, salt and corn syrup in 2-quart saucepan over medium heat, stirring constantly, until sugar is dissolved. Cook, stirring occasionally, to 240F on candy thermometer or until small amount of mixture dropped into very cold water forms soft ball that flattens when removed from water. Remove from heat. Add margarine. Cool mixture to 120F without stirring. (Bottom of pan will be lukewarm.) Add cardamom. Beat vigorously and continuously until candy is thick and no longer glossy, 5 to 10 minutes. (Mixture will hold its shape when dropped from spoon.) Quickly stir in nuts. Spread mixture in buttered 9x5x3-inch loaf pan. Let stand until firm. Cut into 1-inch squares.