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Casseroles contain a mix of meat, vegetables and sauce, and can be made without meat to suit vegetarian palettes. Some casseroles also feature bread crumb and cheese toppings. Lessen the time you spend cooking by making large casseroles and freezing them for future consumption. You can freeze your casserole by placing the whole thing in a large freezer container, or by dividing the casserole into small portions for convenient one-serving meals.

Defrost the frozen casserole. Cover the casserole with wax paper. Place it in the microwave oven and press the automatic defrost setting. "Good Housekeeping" says that your casserole is thawed when the ice disappears. You may need to defrost the casserole for an additional defrost cycle if it doesn't defrost right away, depending on its density.

Reheat the casserole. Press your microwave oven's automatic reheat setting. Set your microwave on high for three minutes, if your microwave oven does not have an automatic reheat setting. Turn the dish containing the casserole halfway through the reheat cycle for even heating (if your microwave does not have an automatic turntable).

Check the casserole temperature using a food thermometer. Insert the thermometer in the center of the casserole first, and then the sides. The USDA says that microwave-reheated food must reach an internal temperature of 165 degrees Fahrenheit to be considered safe for consumption. Continue heating and testing the casserole until it reaches the safe temperature.