Start by spraying your 9x13 baking dish with nonstick cooking spray to ensure easy removal later. Cut your butter into small squares, about 1 tablespoon in size each, for faster and more even melting in the microwave.
Add the mini marshmallows and butter pieces to an extra large mixing bowl or microwave-safe bowl. The bowl should be large enough to accommodate the expanding marshmallows and allow room for stirring the cereal mixture.
Microwave the marshmallow and butter mixture for 2 minutes and 30 seconds, or until the marshmallows have risen near the top of the bowl. Watch carefully to prevent overflow, as marshmallows expand significantly when heated.
Remove from the microwave and stir immediately until no chunks of butter or marshmallow are visible. If you still see lumps after stirring, return to the microwave for 10-second intervals until you achieve a smooth, gooey marshmallow mixture.
Quickly add the Cinnamon Toast Crunch cereal to the bowl and stir rapidly to coat all cereal pieces with the melted marshmallow mixture. Work fast, as the mixture will start to set at room temperature.
Transfer the cereal mixture to your prepared pan and press evenly using clean hands sprayed with cooking spray or a piece of parchment paper. Press firmly but gently to avoid crushing the cereal pieces.
Notes
Timing is Key: The fun part of this recipe is working quickly once the marshmallows are melted. Have your cereal measured and ready to go before you start microwaving for the best results.
Bowl Size: Use an extra-large mixing bowl to prevent marshmallow overflow. If you don't have a big enough bowl, make half the recipe at a time and layer in the pan.
Pressing Technique: Spray your hands with nonstick cooking spray or use plastic wrap to press the mixture evenly without it sticking to your hands or utensils.
Temperature Control: Don't use high heat in the microwave as it can burn the marshmallows. Medium heat or regular microwave power works best for even melting.