Melt butter in microwave safe dish.

Add marshmallows and stir, coating marshmallows with the butter.

Microwave at 50% power for 1-2 minutes, being careful not to overheat marshmallows.

Add Cheerios to mixture, stirring with spoon that has been sprayed with non-stick cooking spray.

Pour Cheerios mixture onto parchment covered half sheet pan.

Use either sprayed palms or sprayed spoon to spread mixture evenly.

Mixture will cover half of a 12x17 pan, may double recipe to cover entire pan.