I made these a couple days ago and they're so good. They're the same as making regular rice crispy treats, but you use cocoa rice crispies instead. They're the perfect gooeyness and the cocoa makes them even better.
In a microwave-safe bowl, heat butter or margarine and marshmallows on High for 3 minutes, stirring after 2 minutes. Remove from microwave and stir until smooth. Add cocoa rice crispy cereal. Stir until well coated (I recommend stirring with a buttered spoon). Using a buttered spatula or waxed paper, press mixture evenly into a 9"x13" pan coated with cooking spray. Cool. Cut into 2" squares and serve.