How to Make It
Preheat oven to 275°F. Line a rimmed baking sheet with parchment paper, and coat with cooking spray.
Whisk together butter, sugar, and cocoa in a large bowl. Add cereals; toss gently to coat. Spread mixture in an even layer on prepared baking sheet. Bake in preheated oven until mixture is tacky but not moist, 15 to 18 minutes, stirring after 10 minutes.
Transfer baking sheet to a wire rack; sprinkle mixture evenly with salt. Cool to room temperature, about 20 minutes.
Transfer mixture to a bowl. Add chocolate chips; toss to combine.