Lightly butter 8*8 pan. In heavy 3 quart saucepan combine sugar, salt, cocoa, milk, and corn syrup. Cook, stirring over medium heat until sugar dissolves. Continue to cook, stirring occasionally to 234 degrees Fahrenheit on a candy thermometer.
Remove from heat. Add butter, do not stir. Let cool to 110 degrees Fahrenheit. Add vanilla. With a wooden spoon, beat fudge until it becomes creamy and is no longer glossy. Quickly stir in nuts.