In a saucepan, melt the butter over low heat. Stir in the marshmallows until melted and combined. Cook for an additional two minutes while stirring constantly. Remove from heat.
Stir in the cereal and chopped Butterfingers until blended and well coated.
Press the cereal mixture into a greased 9X13 pan. Allow to cool and then cut into squares.
Recipe by Sugar, Spice and Family Life at https://sugarspiceandfamilylife.com/2016/03/butterfinger-rice-krispie-treats-recipe.html