Chocolate toffee (scotland)

1 c  Sugar
    2/3 c  Light corn syrup
  1 1/2 c  Half-and-half
  1 1/2    Squares (1 oz each)
           -unsweetened chocolate,
           -melted
  1 1/2 tb vanilla
      1 pn -Salt
 
  YOU SHOULD NEVER TRY TO MAKE TOFFEE (OR ANY OTHER COOKED CANDY, FOR THAT
  MATTER) IN DAMP WEATHER, BECAUSE THE CANDY WILL NOT HARDEN PROPERLY.
  Combine the sugar, corn syrup, and 1/2 cup of cream in a large saucepan set
  over moderate heat. Stir the mixture until the sugar dissolves completely.
  Insert a candy thermometer, reduce the heat to low, and cook the syrup,
  stirring frequently, until the thermometer registers 238F. Blend in another
  1/2 cup of the cream, which will cause the temperature to drop, and
  continue to cook and stir until the thermometer reaches 236 F or until a
  bit of the hot toffee dropped into a little cold water forms a soft,
  pliable ball. Mix in the remaining 1/2 cup cream and the melted chocolate.
  Cook the toffee, stirring constantly lest it scorch. Cook toffee until the
  mixture becomes quite thick: A drop of it should firm up quickly in cold
  water. (NOTE: Even though the temperature of the toffee may not exceed
  230F, if it firms in cold water, remove the pan from the heat at once.)
  Quickly mix in the vanilla and salt, then pour the toffee into a
  well-buttered 8-by-8-by-2-inch pan. Cool the toffee completely, then cut it
  into 1-inch squares. Wrap each one in waxed paper or plastic wrap. Makes 64
  candies.