Make your base Rice Krispies recipe (which is 1 (7 oz) container of Kraft’s Jet-Puffed Marshmallow, 3 T butter, and 6 cups Rice Krispies cereal) according to the box instructions.
Let the mixture cool completely before you add the frosting. I popped it in the fridge for 20-30 minutes, but you could just let it set on the counter for a while.