Melt the butter in a large saucepan over low heat until it’s completely melted and bubbly.

Stir in the marshmallows, mixing them gently until they’re fully melted and gooey.

Add the rice cereal to the melted marshmallow mixture, stirring well until every piece is coated.

Press the mixture into a greased 9x13-inch baking dish using a spatula or your hands.

Let cool at room temperature for about 30 minutes before cutting into squares.