Grease or coat a 13×9 inch pan with non-stick spray.

In a large saucepan, melt butter over low heat. Once melted butter starts to foam (it will turn to a caramel color and smell nutty - watch it closely so that it does not burn), add salt and marshmallows, and stir continuously until the marshmallows are completely melted. Remove from heat and stir in rice cereal.

Using a piece of wax paper or greased spatula, press rice cereal mixture evenly into prepared pan. If using marshmallows and sprinkles, add to the surface and press slightly to adhere. Allow to cool completely before cutting into 2? squares.