The Physical Limitations

• Before you resolve to make your next casserole in the toaster oven, your first step should be to compare the sizes of your toaster oven and casserole dish. Small, traditional toaster ovens can only accept relatively small casserole dishes, while larger and costlier models can sometimes accept pans as large as 9 by 13 inches. The lid is another matter. Compact toaster ovens seldom have enough clearance for the casserole's own lid, so you'll need to use foil instead. Larger models often have room enough to give you the option of using the lid, if that's preferable. If necessary, measure your toaster oven and buy a new baking dish or casserole that fits it well.

A Close Relationship

• A lid, or at least a covering of foil, can be important when you're preparing casseroles in the toaster oven. The heating elements in your regular oven are usually several inches away from the surface of the food, and sometimes 12 inches or more. In your toaster oven, they're much closer, sometimes barely 1 inch. This means your foods will tend to brown more quickly than they should, and can burn if you aren't careful. To minimize the risk, cover them with foil for most of their baking time, even if that isn't called for in the recipe. Remove the foil during the last few minutes, to toast and brown the surface of the casserole before you serve it.

Spills and Thrills

• The toaster oven's rapid browning becomes an advantage at the end of your cooking time, though it can sometimes be problematic. If your casserole is topped with fatty ingredients, such as bacon or sausage, the sputtering fat from the meats will splatter throughout your toaster oven and can become quite messy. At worst, they can meet with the heating element and catch fire. If that happens, unplug the toaster and leave the door closed until the flames die. Open a window and turn on your fan, if you have one. To protect the oven against the fillings boiling over -- a less spectacular but more common occurrence -- place your casserole dish on a small sheet pan, or place a sheet of foil under it.

Special Features

• Appliance manufacturers are always engaged in a competition, adding new features and abilities to make their toaster ovens more versatile and powerful. Many are capable of convection cooking, which can shorten the baking time for your casserole by several minutes. A few include a temperature probe and will alert you when your casserole reaches the correct serving temperature, usually 165 degrees Fahrenheit. High-end models often include infrared broiler elements as well, to brown or toast the top of your casserole even more efficiently.