Butter a 9 x 13 inch baking dish or line with nonstick foil (recommended).

In a large bowl, place chocolate chips and margarine, cut into small pieces. Set aside.

In a large sauce pan, mix together sugar, evaporated milk and a pinch of salt.

Cook over medium heat, stirring constantly until mixture begins to boil.

Continue to cook, keeping at a boil, for approximately 8 minutes or until mixture forms a soft ball when a small amount is dropped into a cup of cold water. A candy thermometer should read about 240 degrees. *Depending on the heat of your stove, this could take anywhere from 7 minutes to 15 minutes; you want to watch closely so that it doesn't burn.

Pour hot mixture over chocolate chips and margarine. Mix well, then beat with an electric hand mixer until creamy.  Add vanilla and nuts (optional). Stir well.  Pour into prepared 9x13" or 11x7" dish.

Cool in refrigerator.  (overnight is best)

Let sit on the counter for about 20 minutes before cutting into squares.