Tear cotton candy into small pieces and set aside. Measure out rice cereal in a separate, large bowl. Grease a 9x13 glass dish with non-stick cooking spray or butter.
Melt butter in a large microwavable safe bowl. Add marshmallows and microwave in 30 second increments stirring each time until the marshmallows are completely melted.
Add in cotton candy a few pieces at a time, stirring until fully melted.
Pour melted marshmallow mixture over the cereal and stir until fully coated.
Firmly press the cereal mixture into the prepared pan. Add sprinkles on top and push into the treats. Allow to sit 30 minutes or until they hold together well. Cut and serve.
Notes
Spray your spoon with non-stick cooking spray to prevent the marshmallow mixture from sticking.
If you do not have a kitchen scale, 1.5 ounces is roughly 3/4 of this 2 ounce tub of cotton candy. The candy melts down like liquid sugar and can thin out your marshmallow mixture so that it won't be sticky and set up so take care not to add too much.
Do not add food coloring to the marshmallow mixture as it, too, will prevent the treats from firming up.
If you would prefer a stronger cotton candy flavor you can add a vial of Lorann Cotton Candy Flavoring to the marshmallows rather than actual cotton candy.