In a large skillet, combine the butter and marshmallows on medium heat. Keep stiring until the marshmallows are completely melted.
In a large mixing bowl, add the rice krispy cereal. When the marsmallows are completely melted, stir that into the cereal. Gently fold in the sprinkles.
Spread the mixture into the baking dish and gently pat down - make sure it is even all around.
Recipe Notes
*If you would like thicker bars, you can use a 8x8 baking dish. It will only make 9 bars.