Line a 9x13-inch baking pan with foil and spray with cooking spray. Set aside.

Melt the butter and the marshmallows in a medium sized saucepan over medium-low heat. Once the marshmallows are melted, remove from heat and stir in the vanilla. Quickly stir in the cereal. Stir in the candy and sprinkles.

Pour the marshmallow-cereal mixture into the prepared baking dish. Press to flatten. (I like to spray my hands with cooking spray and use them to press the treats into the pan – just be careful not to burn yourself.) Cool completely before cutting into squares.