PLACE sugar, peanut butter, butter and salt in large mixer bowl. Beat until smooth. Stir in chopped Butterfinger.
PLACE morsels in large, microwave-safe bowl. Microwave on HIGH (100%) power for 1 minute; STIR. The morsels may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring until morsels are melted.
COAT inside sides and bottoms of baking cups with melted chocolate using a small spoon or paintbrush. Transfer cups to mini muffin tin(s); freeze for 10 minutes or until set.
REMOVE about one-third of chocolate cups from freezer. Spoon peanut butter mixture into cups, filling each about three-fourths full. Spoon melted chocolate over mixture, covering completely and filling cups to the top. Return to freezer; repeat with remaining cups. Freeze for 20 minutes or until set. Serve immediately or store in tightly covered plastic container in freezer for up to 2 weeks. To serve, remove from freezer and let cups stand for a few minutes. Peel off cup and serve cold.
HELPFUL HINTS: Cool chocolate for about 5 minutes after melting so that it is easier to work with. Set bowl of melted chocolate over pan of warm water (being careful not to get any water into the chocolate) to keep it a nice consistency for coating foil cups.