Remove the marshmallow mixture from the heat and pour over the bowl filled with the Rice Krispies cereal. Add the mini marshmallows and the mini chocolate chips and fold the two together again.
Transfer the mixture to the prepared baking dish and press into the pan evenly. Let the treats sit at room temperature for about an hour before eating.
It’s helpful to use a small piece of parchment paper to press the bars into your pan. You can also use a little bit of butter on your fingers to prevent sticking. Be careful, the mixture is hot!