Mix sugar, corn syrup, water, cornstarch, butter, and salt. Heat to boiling over medium heat, stirring constantly.

Cook without stirring until a small amount dropped into cold water forms a hard ball, or the mixture reaches 256°F on a candy thermometer.

Remove from heat, add vanilla, and pour into a pan.

When cool enough to handle, butter your hands and pull the taffy until satiny and stiff; the color will lighten.

Pull into 1/2-inch-wide strips, cut into pieces about 1 1/2 inches long, and wrap in waxed paper.