Combine sugar and cornstarch in a large saucepan.

Add corn syrup, butter, water, and salt to the saucepan.

Cook the mixture rapidly over medium-high heat.

Continue cooking until the mixture reaches the hard-ball stage (250-266°F) when tested in cold water.

Pour the hot candy onto a lightly buttered shallow pan.

Let the candy stand undisturbed until it is cool enough to handle.

Sprinkle vanilla extract over the surface of the candy.

Optionally, add nuts at this stage.

Pull the taffy with your hands until it becomes white and glossy.

Lay the pulled taffy on waxed paper in a long rope.

Cut the rope into bite-sized pieces.