Line an 8x8-inch baking pan with parchment paper, leaving an overhang on the sides for easy removal.
In a medium saucepan over medium heat, melt the butter and peanut butter together, stirring until smooth.
Remove from heat and stir in the vanilla extract.
Gradually add the powdered sugar, mixing until fully combined and smooth.
Press the peanut butter mixture evenly into the prepared pan.
In a separate microwave-safe bowl, combine the chocolate chips and heavy cream. Microwave in 30-second intervals, stirring between each, until smooth and fully melted.
Pour the chocolate mixture over the peanut butter layer and spread evenly.
Refrigerate for at least 2 hours, or until firm.
Lift the fudge out of the pan using the parchment overhang and cut into 24 squares.
Store in an airtight container in the refrigerator for up to 2 weeks.
Notes
For best results, use high-quality chocolate chips and creamy peanut butter without added sugar or stabilizers.