- Line a 13×9-inch casserole dish with parchment paper and lightly coat with no-stick cooking spray. Set aside
- Place rice cereal and fruity cereal in an extra large bowl, toss to combine, and set aside.
- Combine sweetened condensed milk, 3/4 of the marshmallows, and white chocolate chips in a large bowl, set the bowl over a large pot filled 1/4 full with water creating a double boiler. Heat over medium, stirring consistently, until melted and smooth.
- Pour the melted mixture over the cereal, add the remaining (unmelted) marshmallows, and stir to coat and combine.
- Transfer to the prepared casserole dish, evenly spread the coated cereal to the edges, and gently press to compact. Set aside to cool and harden before cutting into squares.