Cook remaining ingredients except butter in a 3-quart saucepan over medium
heat, stirring constantly, until sugar is dissolved. Clip a thermometer to the side
of the saucepan. Cook, stirring occasionally, to 234 degrees F.
Remove saucepan from heat. Stir in butter.
Cool mixture without stirring to 120 degrees F. (Bottom of saucepan will be lukewarm.)
Beat vigorously and continuously with spoon or heavy electric mixer 5 to 10 minutes
or until candy is thick and no longer glossy. Mixture will hold its shape when dropped
from a spoon.