Line an 8-inch square baking dish with parchment. In a microwave-safe bowl, melt candy corn in 30-second intervals, stirring between each one, until completely melted, about 2 1/2 minutes total. Stir in peanut butter until smooth. Pour into baking dish and smooth top with an offset spatula. Let stand to cool and firm up, about 1 hour.
Pull up corners of parchment to remove candy from baking dish. Cut candy in half crosswise, then into 1-inch bars. Put candy melts in a microwave-safe bowl and heat on 50 percent power until melted and smooth, stirring every 30 seconds. Line a baking sheet with waxed paper.
Using a small offset spatula or butter knife, spread a thin layer of candy melts all over bars. Place on baking sheet and sprinkle with nonpareils, if desired. Let stand until candy coating hardens, 10 to 20 minutes. Serve immediately or store in an airtight container in the refrigerator.