Heat the butter and peanut butter in a microwave safe bowl in 30 second intervals, stirring between each interval, until melted. It took mine 1 minute 30 seconds to melt.
Add the powdered sugar ½ cup at a time, stir between each addition.
Spread the mixture in a parchment paper lined 8x8 baking dish. Press into an even layer.
Top with mini chocolate chips, pressing the chips lightly into the fudge.
Chill for at least two hours, then slice into one-inch pieces before serving.
Notes
Storage: Store in an airtight container in the refrigerator for up to two weeks with parchment paper between layers.