Melt butter and let cool for 15 minutes
Beat peanut butter and melted butter using a whisk or hand mixer until well-combined
Gradually beat in powdered sugar until combined
Fold in crushed graham crackers using a rubber spatula
Spread mixture into a square pan lined with foil or parchment paper, chill in fridge for 1 hour
Melt chocolate chips using either microwave or double boiler
Spread evenly over top of the bars, chill overnight
Remove bars from pan and cut into 2x2" squares, store in the fridge, they'll keep for 1-2 weeks in an airtight container