To make cups: Heat chocolate chips over double boiler or in microwave until just melted. Don't overheat, stir until smooth. Set candy cups on cookie sheet, fill about1/4-1/3 full with melted chocolate. Use spoon or very small spatula to pull melted chocolate up sides of cup. Place cookie sheet in freezer 2 minutes to harden.
While cups harden, start making filling. Mix peanut butter, confectioners sugar and melted butter till well combined. Chill filling.
Roll filling into balls to fit inside chocolate cups and still leave room for a coating of chocolate on top. Press peanut butter ball gently into cup to get rid of airspaces. Spoon more melted chocolate on top to cover; spreading in a swirling fashion for a nice design on top. Chill to harden.
Store in airtight container in cool place or refrigerator.
Try other fillings too. Try using a little less peanut butter filling and add your favorite jelly. Or just your favorite jelly by itself. Be creative, there are many thing you can fill your cups with including: marshmallow fluff, fruit pie fillings, melted caramels, nuts, candies, etc...