Ideally, you should clean your casserole after each use. However, if it's not particularly dirty, you can get away with cleaning it once a week. If you do need to clean it more often, be sure to dry it thoroughly after each washing to prevent rusting.
Utensils are a great way to cook food in an oven. They're simple to use and can be made from a variety of materials. Be sure to clean your steel cookware regularly to keep it in good condition.