Spray a 9x13-inch baking dish with nonstick cooking spray (this will just help get the bars out easier).
In a large pot over medium heat, melt butter with mini marshmallows. Don't allow to burn.
Stir frequently and melt gently until smooth and combined. Take pot off of heat.
Stir in Cinnamon Toast Crunch cereal. Stir until mixture is totally combined. This will take a few minutes.
At this point, you can stir in chocolate chips. They will melt as you stir them in. Or, if you want to keep them more intact, transfer mixture to another bowl (this will help it cool faster). And then wait a few minutes before stirring in chocolate chips.
Pour mixture into prepared baking dish and spread out evenly.
Allow mixture to cool completely and then slice.
Video
Notes
Golden Grahams can be substituted for the Cinnamon Toast Crunch.