Line 24 small muffin cups (1-3/4 inches in diameter) with small paper bake cups. Remove wrappers from chocolates.
Place 48 chocolates in small microwave-safe bowl. Microwave at MEDIUM (50%) 1 minute; stir. Microwave at MEDIUM an additional 10 seconds at a time, stirring after each heating, just until chocolate is melted when stirred. Using small brush, coat inside of paper cups with melted chocolate.
Refrigerate 20 minutes; reapply melted chocolate to any thin spots. Refrigerate until firm, preferably overnight. Gently peel paper from chocolate cups.
Beat peanut butter, powdered sugar and butter in small bowl until smooth. Spoon into chocolate cups. Before serving, top each cup with a chocolate piece. Cover; store cups in refrigerator. About 24 servings.