1. Prepare the dish, as you would if you were preparing it fresh.
2. Place the dish in the serving dish you will use, as long as the serving piece is oven and freezer proof. If the serving piece cannot go in the oven, then use some sort of pyrex or likewise dish.
3. Allow the dish to cool thoroughly. Do not skip this step.
4. Cover the dish tightly with two layers of aluminum foil.
5. Defrost the dish completely in the refrigerator or that morning before you need it.
6. Reheat the dish completely at 250 degrees for about one to one and a half hours. Test to see if the dish is thoroughly heated.
7. Uncover the dish and turn up the oven to 350 degrees for 10 to 15 minutes.
Your dish will be perfectly lovely. If I reheat mash potatoes, I fluff the mashed potatoes with a fork and taste to see if it needs salt or pepper. Your guests will never know and you will have time to spend with everyone instead of stressing over the dinner.
The absolute biggest bonus for me... The kitchen is absolutely clean and I am relaxed!!!