Best Ever Chicken Casserole

1 . Stage

Preheat the oven to 350 degrees F (175 degrees C).

2 . Stage

Bring a large pot of water to a boil. Cook chicken in boiling water until no longer pink in the center and the juices run clear, 12 to 15 minutes. An instant-read thermometer inserted into the center of each breast should read 165 degrees F (74 degrees C). Drain, then cut chicken into bite-sized pieces.

3 . Stage

Mix together chicken pieces, onion, condensed soup, water chestnuts, mayonnaise, and most of the cornflake crumbs in a large bowl until well combined. Pour into a 9x13-inch casserole dish. Sprinkle with remaining cornflake crumbs.

4 . Stage

Bake casserole in the preheated oven until heated through and the top is golden brown, about 1 hour.