Combine sugar, syrup, salt, chocolate and 1 cup cream in large heavy saucepan. Stir constantly until mixture comes to a full boil. Gradually add remaining cream so that boiling does not stop. Continue cooking, stirring constantly, to firm-ball stage (248~F.). Remove from heat. Stir in vanilla extract and nuts. Pour into buttered 8 inch square pan. When cold, turn out on cutting board and cut into 3/4 inch squares.