Melt the butter in a microwave-safe bowl. Once melted, add the marshmallows and microwave for about 20 seconds, depending on the strength of your microwave. Watch closely! The marshmallows will start to puff up; don’t let them go over the edge.
Remove from the microwave (marshmallows will deflate) and stir the melted butter and marshmallows together until smooth.
Mix in your favorite cereal and stir until well combined. If desired for shape, transfer it into another container. Let sit for 10 minutes.
Once cool, you can pop it out, cut it up and enjoy...or it eat straight from the container!