In 3-quart saucepan, combine sugar, marshmallow creme, evaporated milk, butter, and dash salt.
Cook and stir over medium heat till mixture boils.
Boil gently, stirring frequently, for 5 minutes.
Divide mixture in half.
To one half (about 3 cups) add chocolate pieces; stir to melt and blend.
Pour into buttered 13 x 9 x 2-inch pan.
To remaining half of marshmallow mixture, add the butterscotch pieces, beating till smooth.
(If necessary, beat butterscotch mixture with rotary beater till pieces are melted and mixture is smooth.) Pour over chocolate layer; cool.
Cut in pieces.