Melt butter in a large saucepan over low heat and add marshmallows.
Once melted, stir the cake mix slowly into the melted marshmallows until it is combined.
In large bowl, combine the rice krispies and melted marshmallow mixture. (I just used a large pot for melting the marshmallows, removed from heat and added the rice krispies at this time and mixed together.)
Add 1/2 of the sprinkles to the marshmallows and rice krispies while stirring.
Spray a 9x13 with cooking spray and press it down into the dish.
Sprinkle the remaining sprinkles on top.
Wait about 30 minutes before cutting and I also sprayed the knife with cooking spray to help them cut easily!
Notes
*With the remaining cake mix you can also made some cake batter cookies. All you would have to do is measure 6 oz of cake mix and 1/4 cup canola oil and 1 egg. Form that into balls and bake at 350 for 10-12 minutes.