Line a baking sheet with parchment paper or a silicone baking mat and set aside.
In a microwave safe bowl, combine chocolate chips, peanut butter chips and vegetable oil. Microwave in 30 second intervals, stirring in-between, until melted and smooth.
Pour half of the melted chocolate mixture onto your prepared baking sheet and spread into a rectangle that is roughly 9x13 inches in size. Transfer to the fridge or freezer to harden.
In the meantime, combine creamy peanut butter, softened butter, vanilla extract, and powdered sugar. Mix until well combined.
Drop pieces of the peanut butter mixture all over the layer ofchilled chocolate, then press into an even layer.
Pour the remaining melted chocolate mixture on top, then spread to cover the peanut butter layer.
Sprinkle Reese’s pieces candies on top, then transfer back to the fridge or freezer to set completely before breaking into pieces.