Grease or spray an 11 x7-in. pan with butter or non-stick cooking spray.

In a large microwave-safe bowl, combine the butter and marshmallows and place the bowl in the microwave. Heat on high for 1 minute and 30 seconds.

Immediately stir well until the butter is fully mixed into the marshmallows.

Quickly add the cereal and mix well until the cereal is fully covered.

Pour the cereal mixture into the prepared pan, spreading it evenly, and pressing it down to compact the mixture slightly.

Evenly shake the sprinkles over the top and lightly press them against the marshmallow so they stay stuck.

Cover with plastic wrap and let sit for about 4 hours or until hardened and easily cut without being gooey.