Combine sugar, evaporated milk and dash of salt in large saucepan. Boil over medium heat 14 minutes, timing after mixture comes to full boil. Stir occasionally. While syrup is cooking, place butter, chocolate pieces and dash of salt in large mixer bowl. After syrup is cooked, pour over chocolate-butter mixture in bowl and blend at low speed first, then beat at high speed 10 minutes. Add nuts and vanilla and stir to blend. Pour fudge into greased 13x 9-inch pan and chill until firm. Makes about 4 pounds