Line an 8x8 inch baking dish with parchment paper, leaving some overhang on the sides.
In a microwave-safe bowl, combine the semi-sweet chocolate chips, sweetened condensed milk, and butter. Microwave in 30-second intervals, stirring in between, until fully melted and smooth.
Fold in the chopped Butterfinger candy bars until evenly distributed.
Pour the fudge mixture into the prepared baking dish and spread it evenly.
Refrigerate for at least 2 hours or until fully set.
Lift the fudge out using the parchment paper overhang, cut into squares, and enjoy!
