In a large, microwave-safe bowl, add 2 bags of mini marshmallows & 3/4 Cups very softened butter (slightly melted is great...basically we don't want cold hard butter straight from the fridge).
Cook marshmallows in the microwave until completely melted. To avoid overcooking your marshmallows, use 30-second increments to ensure they are being watched closely. Stir each time your 30 seconds end
Once the mixture is soupy and smooth, it's done. This process does not take long!!!Make sure the butter and melted marshmallows are thoroughly mixed so your treats are not tough
Start adding your rice crispy cereal a little at a time.Keep adding and mixing until you've reached the desired consistency. You want to keep a nice balance of cereal to marshmallow mixture. The cereal should be coated evenly and your mound of rice crispy treat should feel nice and firm, but able to be shaped
Pat treats into a greased jelly roll sheet pan.
Let cool completely before cutting out heart shapes.