Refrigerate for 45 minutes or until firm. Line two cookie sheets with parchment paper.
In double-boiler, melt milk chocolate and shortening. Dip balls and coat thoroughly. With slotted spoon, lift balls out of chocolate and let excess chocolate drip off. Place on parchment-lined cookie sheet. In separate double boiler, melt white chocolate. Using a fork, drizzle white chocolate over balls. Let cool. Store in airtight container, in refrigerator.
Stir together powdered sugar, peanut butter and butter until well mixed. Shape peanut butter mixture into 1 inch balls, placing them on a baking sheet covered with waxed or parchment paper. Let balls stand for 20 minutes until dry. Melt the chocolate chips and shortening in a double boiler. Drop balls one at a time in melted chocolate. Using a fork, remove from the chocolate, letting excess chocolate drip off. Place back on the waxed paper. Let dry about 1 minute, then sprinkle with chopped nuts if desired. Let stand until dry. Store tightly covered in a cool dry place.