In a very large pot, combine jumbo marshmallows and butter.
Heat over medium heat, stirring frequently, until smooth and melted.
Remove from heat and add Cinnamon Toast Crunch Cereal and mini marshmallows. Stir until everything is coated with melted marshmallow-butter mixture.
Immediately pour this mixture into prepared 9x13 pan and press down gently to flatten. (You might want to spray some non-stick cooking spray on your hands to do this.) Don’t press them down too much or they will get tough.
Let cool and harden at least 15 minutes before cutting into bars and serving.