Line two large baking sheets with parchment paper. Set aside.
Combine the4 cups crispy rice cereal and 1 cup mini marshmallows in a large bowl. Mix with a rubber spatula until combined. Set aside.
Melt the 10 oz. white chocolate melts (or white chocolate chips) in the microwave in 30-second bursts. Stir after each round until smooth and completely melted. (Mine took about 2 minutes. Keep an eye on it because you do not want them to burn.)
Add the 1 cup creamy peanut butter to the melted white chocolate, and stir until smooth.
Pour the warm white chocolate-peanut butter mixture on top of the crispy rice cereal mixture. Stir until completely coated.
Add any Additional mix-ins (add ½ - ¾ cup total), if desired, and stir until incorporated.
Scoop the cookies onto the prepared baking sheets with a 1-tablespoon cookie scoop or a spoon. They will be sticky and messy, and this is OK.
Add extra toppings, if desired.
Refrigerate for 30-45 minutes, or until the white chocolate mixture is set.
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