In a large pot, melt the butter over low heat until completely melted.
Add the mini marshmallows and the marshmallow cream to the melted butter and continue to cook over low heat, stirring constantly, until combined and smooth.
Slowly add the rice crispy cereal, stirring to make sure all of the cereal is coated with the marshmallow mixture.
Gently press into a greased 8x8 square pan, or 9x13 if you prefer your thinner rice crispy treats.
Let the treats cool completely.
Cut and serve!
Notes
Store your leftovers (if you have any) in an airtight container.