Line two baking sheets with parchment paper. Arrange the unwrapped Reese's Peanut Butter Cups on the parchment, leaving a little space between each one. Set aside in a cool place.
Place the white chocolate bark in a 4–6-quart slow cooker.
Add the roasted salted peanuts.
Sprinkle the peanut butter baking chips over the peanuts.
Cover and cook on low, checking after 30 minutes. Gently stir and continue heating in 10–15-minute intervals until the peanut butter chips and white chocolate are just melted and the peanuts are evenly coated. Depending on the slow cooker, this may take approximately 45–90 minutes. Do not leave the mixture cooking unattended.
Turn the slow cooker off as soon as everything is melted and smooth.
Allow the candy mixture to cool for a few minutes so it is warm and spoonable rather than very hot. If necessary, stir occasionally as it cools.
Spoon approximately 1 heaping tablespoon of the peanut mixture over each Reese's Peanut Butter Cup, spreading it gently so it covers most of the top. Work carefully so the peanut butter cups don't melt excessively.
Melt the milk chocolate wafers in a microwave-safe bowl according to package directions, stirring until smooth.
Transfer the melted chocolate to a small zip-top bag and snip off one tiny corner, or use a spoon to drizzle chocolate over each candy.
Allow the candies to set at cool room temperature, or refrigerate for approximately 20–30 minutes until firm.
Once completely set, transfer the candies to an airtight container.