1. Spray a 9×13 baking dish with cooking spray; set aside.
2. Melt the 3 tablespoons of butter and the marshmallows over low heat stirring occasionally.
3. Once melted remove from head and pour in the cereal.
4. Use a large spoon to stir the mixture and completely coat the cereal.
5. Pour the mixture into the prepared baking dish. Distribute evenly and press down into pan.