In a heavy saucepan over medium heat, bring the sugar, salt, butter and evaporated milk to a boil. Boil for 6 minutes.
Meanwhile, place the pecans, marshmallow fluff and chocolate in a large bowl. Pour the boiled syrup over the chocolate mixture. Beat until chocolate is all melted.
Spray a 15 1/2 by 10 1/2 by 1-inch jelly-roll pan with a nonstick cooking spray and pour fudge into pan. Let harden at room temperature before cutting into 1-inch squares (can be placed in the refrigerator or freezer to speed hardening process).