Place butter and marshmallows in a microwave-safe bowl; microwave for one minute.
Quickly stir in peanut butter and remaining ingredients in the order listed.
Add Cheerios and mix well.
Use wet clean, fingers to press into a 9 x 13 pan lightly coated with butter or non-stick cooking spray..
Notes
Have all ingredients measured out before starting the microwave because the marshmallows will set up fairly quickly
We like to reserve a few M&Ms to sprinkle on top, but they must be added and pressed down quickly to stick
Regular or Honey Nut Cheerios work well in this recipe
Make sure cereal is fresh, I may have used slightly stale cereal before which makes the bars taste stale
All cooking appliances and conditions are different, so you should test these times and guidelines first in your own appliance to determine what adjustments may be needed!