How to heat frozen casseroles

Updated March 23, 2017

Although a microwave oven is the fastest way to defrost and heat frozen food, you can just as easily heat your casserole in a conventional oven or on a hob. It takes longer to heat food in conventional ovens or on a hob, and you should plan ahead if possible to defrost your casserole before heating it. Keep a meat thermometer on hand to check your casserole. Your casserole is safe to eat when the temperature reading is about 74 degrees C (165F).

Microwave method

Unwrap the casserole and place it in a microwave-safe casserole dish. Cover the dish with microwave-safe cling film. Set the microwave on "Defrost" for six minutes. If your microwave has a preprogrammed "Defrost" setting then you don't need to manually set the timer.

Set the microwave on "Reheat" for about two or three minutes. Open the door halfway through the set time, and stir the casserole to evenly distribute heat. If your microwave has a preprogrammed "Reheat" setting then you don't need to manually set the timer.

Put the casserole back in the microwave and set "Reheat" again if the casserole is still icy in some sections. When the reheat cycle is over, allow the casserole to sit in the oven for about three minutes before you open the door. Insert a food thermometer in the middle and side areas of the dish to make sure that the casserole is ready and safe to eat.

Oven method

Remove the casserole from the freezer and put it in the fridge to thaw for approximately 24 hours before you plan to heat it. If you did not plan ahead, you can put the frozen casserole directly in the oven. It takes approximately twice as long to heat completely frozen food than it takes to heat partially thawed food.

Preheat the oven to 180 degrees C (355F). Put the casserole in an oven-safe baking dish. Cover the baking dish with aluminium foil. Set the oven timer for 30 minutes. Check the casserole by using a fork after 20 minutes to see if it is soft through to the bottom. Close the oven door and allow it to continue heating for the remaining 10 minutes.

Insert a thermometer in the centre of the casserole and in several spots along the edges to check if it's at a safe temperature to eat. Set the oven timer for another 15 minutes and put the casserole back in the oven if the casserole needs additional heating.

Hob method

Remove the casserole from the freezer and put it in the fridge to partly thaw for approximately 24 hours. If you did not plan ahead, place the casserole in a watertight plastic bag, and submerge it in a saucepan of cold water for about 30 minutes to soften the ice.

Place the casserole in a saucepan on the largest burner on your hob. Add 50 ml (1/4 cup) of water to the bottom of the pan to keep the casserole from sticking. Set the hob burner to a medium heat. Set the timer to 10 minutes.

Check the casserole every five minutes using a fork and heat-resistant spatula. Gently lift the edges of the casserole to make sure it is not sticking to the pan. Add a little more water to the pan and turn the burner down to a low setting if the casserole is sticking. Use the thermometer to make sure the casserole is a safe temperature for eating. If the casserole is not thoroughly heated after 10 minutes, leave it on the hob for another five to 10 minutes.


Don't leave the room while your casserole is heating.

Never put foil in the microwave.

Never put any dish in the microwave that is not microwave safe.

Always use an oven glove to touch baking dishes.

Things You'll Need

  • Microwave-safe casserole dish
  • Microwave-safe cling film
  • Meat thermometer
  • Fork
  • Oven-safe baking dish
  • Aluminium foil
  • Watertight plastic bag
  • Saucepan
  • Heat-resistant spatula
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About the Author

Based in Reston, Va., Lydia King has been a writer and editor since 1996, working with diverse subject matter including law, government contracting, philosophy and career guidance. She completed a Bachelor of Arts in history at National University, where she is pursuing a Master of Arts in English and comparative literature.