cook to 270 F, remove from the heat and add:
Recook to 270 F for soft butterscotch, or 300 F for hard butterscotch.
After adding the butter cook slowly and stir constantly as it becomes very thick and is easily scorched. Pour by the spoonful onto buttered foil to make patties, or pour into and eight inch square (buttered) pan for squares. Score the squares deeply as soon as the candy is hard enough to hold the impression, then break apart when the candy has cooled to room temperature. Wrap individually and store in an airtight container.