Gather 3 tablespoons butter, 1 package marshmallows, 6 cups crispy rice cereal, and a greased 9×13-inch pan
Melt the butter in a large pot over low heat
Add the marshmallows and stir until completely melted
Remove from heat
Stir in the crispy rice cereal until evenly coated
Press the mixture into the greased pan using a buttered spatula or wax paper
Let cool for about 30 minutes
Cut into squares and serve