Get your ingredients and supplies ready to go.
(optional) lightly grease the inside of your mug with a little butter or a few sprays of non-stick cooking spray.
Put ½ tbs of butter in the mug.
Put 6 marshmallows in the mug.
Put 1.25 cups of rice krispie cereal in the mug.
Heat in the microwave for 20 seconds.
Remove and stir. If not fully melted, add another 5 seconds of heating and stir; repeat til fully melted.
Enjoy!