"I used to make a batch of these every two days for my cafe. They were extremely popular and always sold out. A delicious and light chocolate square that packs well in lunches. I like to make for Halloween treats by simply scattering Reese's pieces over the top and pushing into top of square while still warm in pan. Enjoy!"
Combine marshmallows, brown sugar, corn syrup, cocoa powder, and butter in a small saucepan; cook and stir over medium-low heat until smooth and bubbling. Remove saucepan from heat and stir in vanilla extract.
Pour chocolate mixture over cereal and stir until evenly coated. Press cereal mixture into the prepared baking dish and cool for 10 minutes. Turn cereal mixture onto a work surface and cut into 12 or 24 squares using a serrated knife. Individually wrap squares in plastic wrap or store in an airtight container.