Never tried brain, but yes they're breaded and fried like liver, gizzard, or heart. You may be surprised at the size of them. I slow-grow my CX on restricted diets for better flavor though. They can live a much healthier life on limited commercial feed and forcing them to browse on natural foods, and they taste better IMO.
ETA that I'm probably done with growing CX; I'm breeding quality Cornish as a sustainable meat breed [a WC is my avatar] and working on a large blue/green egg layer [a mix of CX, Ameraucana, and true Cornish] as a small flock of dual purpose chickens. Show quality Cornish have a beautiful shape and great flavor as a table bird, but poor layers of small eggs; my crosses will serve as egg layers plus the culls are very meaty and faster growing than Cornish.