Lightly crush the potato chips with your hands and set aside.
Melt the butter in a large pot over medium-low heat. Add 1½ bags of mini marshmallows and stir until completely melted and smooth.
Fold in the crushed potato chips until fully coated in the marshmallow mixture. Add the remaining mini marshmallows and gently fold them in.
Transfer the mixture to a parchment-lined 8x8-inch pan and gently press into an even layer. Let set completely before slicing and serving.