In a large saucepan, combine butter, evaporated milk, and granulated sugar. Cook over medium heat, stirring constantly, until the mixture comes to a rolling boil.
Boil without stirring for 5 minutes. Remove from heat.
Stir in the marshmallow creme and vanilla extract until smooth.
Stir in the chopped Butterfinger bars.
Pour the fudge into the prepared pan and spread evenly.
Let cool completely at room temperature, then cut into squares.
Notes
Store in an airtight container at room temperature.