In a mug, add butter and microwave for 15-20 seconds or until just melted. Tip the mug slightly to the side and roll the melted butter around to coat the edges a bit.
Add marshmallows and microwave again for 30 seconds. Carefully remove from microwave and stir to combine. Immediately add Rice Krispies cereal and stir to combine. Start with ½ cup, then add up to another ¼ cup more if you'd like it thicker.
Serve and enjoy!
Cereal to marshmallow ratio: Start with ½ cup of Rice Krispies cereal at first, then add more if you want it to be thicker. I prefer my ratio of cereal to marshmallow to be more marshmallow-heavy, and it's also easier to eat with a spoon.Mug size: You want your mug to be at least 8 ounces.Microwave wattage: My microwave is 1500 watts, so you may need to adjust your time to be less or more depending on the wattage of your microwave.