Spray a 9x9 pan with non-stick spray, and then sift 1/4 cup of
the powdered sugar mixture into the pan, tilting to coat all the edges with the powdered mixture.
Then dust the cake with a sifter with
the powdered sugar mixture to help it to set (this is exactly what you would use to help marshmallows set too).
Close the bags and shake the cereal to coat it in
the powdered sugar mixture.