Preheat the oven to 325 degree F.
Bring a medium pan of salted water to a boil and cook the chicken breasts in it until the center is no longer pink.
Remove the breasts, cool and shred them and set aside. Reserve 2 cups of the water.
Add the 2 cups of water, celery and rice into a skillet and cook until the water is absorbed.
Add the chicken, cream of chicken and mayo to the rice and celery and stir.
Transfer to a 9 x 13" baking pan.
Top with the cornflakes and drizzle with melted butter before baking for one hour.
Let it cool for at least 10 minutes before serving!