Spray PERFECT BROWNIE pan and divider thoroughly with nonstick cooking spray.
Melt butter in large saucepan. Add marshmallows and stir constantly until melted. Pour over rice cereal and stir until well coated. Immediately spread mixture into PERFECT BROWNIE pan and press divider into treats.
If desired, top with M&M candies or sprinkles while treats are still warm. Lightly press candies onto marshmallow treats to secure.