Melt stick of butter in a 9 x 13-inch (22 x 33 cm) glass casserole dish.
Stir the rice, corn, onion, water chestnuts, sour cream, and cream of chicken soup together until mixed well. Pour mixture into casserole dish and spread it out evenly. The butter may spill onto the top of the casserole and that’s fine.
Bake uncovered for at least 20 minutes. Depending on your oven it may need to cook longer if you have a cold cooking oven. The center of the casserole must reach a hot temperature to your touch.
Remove from the oven. Sprinkle the shredded cheddar cheese on top of the casserole and cook for 10 minutes, or until the cheese is melted well.
I hope you enjoy our family favorite casserole! We take it to church dinners and never have any leftovers. It can be made ahead of time and frozen for cooking on those busy holidays!