Line a cookie sheet with parchment paper and set aside.
Warm a sauce pan over medium heat.
Grease pan with cooking spray.
Pour Reese's chips into warmed sauce pan.
Stir constantly, until chips are fully melted. About 3 minutes.
Pour the melted chips onto the prepared cookie sheet.
Use a rubber spatula to spread the chips out evenly over the parchment paper.
Top the melted chips with the Reese's Pieces and halved mini peanut butter cups.
Place the candy into the fridge to cool, about 1 hour.
Once the bark is fully cooled and hardened, break into pieces and enjoy.
Store in any uneaten leftovers in an air-tight container, up to 3 days.