In a medium saucepan over medium heat, combine the mini marshmallows and butter.

Stir until the mixture is melted, then remove from heat.

Coat a large bowl lightly with cooking spray, add the cereal and marshmallow sauce, stir until the cereal is well coated with the sauce.

Add the cereal mixture to a small casserole dish that has been coated with cooking spray.

Spread with a spatula (one that’s been coated with the spray is helpful since this mixture gets sticky!) until one even layer.

Refrigerate for at least one hour before cutting into treats.