Gather 3 tablespoons butter, 1 package marshmallows, and 6 cups crispy rice cereal
Grease a 9×13-inch pan
Melt the butter in a large pot over low heat
Add the marshmallows and stir until fully melted and smooth
Remove from heat
Add the crispy rice cereal
Stir until evenly coated
Press the mixture into the greased pan
Let cool until set
Cut into bars