Line a 9x13 inch baking pan with parchment paper and set aside.
In a large bowl, cream together the butter, peanut butter and vanilla until smooth. Add in the powdered sugar, and mix until fully combined.
Spread the mixture evenly over the prepared baking pan, pressing down with a silicone spatula. Place in the fridge.
In a microwave safe bowl, microwave the chocolate chips and coconut oil in 30 second intervals, mixing until smooth.
Pour the melted chocolate overtop the peanut butter mixture and smooth with a spatula. Return to the fridge until the chocolate has hardened. Cut into bars.
Notes
Storage: Store any leftover bars in an airtight container at room temperature for up to 2 days, or in the fridge for up to 3 weeks.
Freezing: These bars freeze very well. Place them in a freezer-safe container and freeze for up to 3 months. When ready to eat, thaw in the fridge or at room temperature.
To prevent the chocolate from cracking, allow the bars to sit for around 10-15 minutes at room temperature. Run a sharp knife under hot water then wipe dry before cutting.
Do not use natural peanut butter! This will cause the mixture to be more liquid, which will prevent the bars from holding their shape.