Line 15 x 10 x 1 inch jellyroll pan with aluminum foil; set aside.
Put butter into 2-quart saucepan; melt over low heat; add sugar. Put candy
thermometer in pan. Stir over moderate heat until mixture becomes pale caramel
color and candy thermometer reaches 300 degrees F, about 10 minutes.
Remove from heat; spoon evenly into foil-lined pan. Cool for 5 minutes.
Scatter butterscotch pieces evenly over candy. As soon as they are soft,
about 4 minutes, spread with back of teaspoon over entire surface.