Every Year we end up with lots of food (naturally) that we prepared for holiday dinner and that no one ate. It's a Jewish tradition to make sure that there's plenty of food and that seems to mean there's plenty of leftovers.
Some of them are good leftovers. There's no trouble getting rid of leftover chopped liver or matzo ball soup. Some leftovers are perfectly good, it's just that no one particularly wants to eat them. Since none of us want to throw them out (another Jewish tradition), figuring out how to be inventive could be considered part of surviving Passover. Here are a few of the tricks I've come up with over the years.
Everything depends, of course, on what you decided to serve. Our main courses usually rotate between roasted chicken(s), brisket, roast beef, and leg of lamb. If we have a lot of people coming, we sometimes make two main courses just to make sure everyone's happy.
Roast chicken is usually the least problem. It's good eaten cold (or at room temperature). My rule is don't reheat it unless you're putting it into some kind of sauce -- it gets too dry. We do sometimes cut it up and make it into a Chicken Tetrazinni. Very old fashioned. If you're Kosher, you can make this with a milk or cream substitute. Cut up the chicken into large chunks (1" is good). Make a medium white sauce (2 tablespoons of butter or margarine to 2 tablespoons of flour or potato starch to 1 cup of milk o milk substitute). You need about oone cup of white sauce to every cup of chicken. Cook 2 cups of Passover noodles (yes, they have them now) lightly, drain, and mix with the white sauce, which you have seasoned with salt and pepper and freshly grated nutmeg. Mix in the chicken. If you like you can also add some cut up, cooked, broccoli, spinach (well drained), or aspargus. Place all into a buttered or sprayed casserole and place in a 350 oven for about 20 minutes until heated through and bubbling.
You can also take leftover roast chicken and use it in the Lamb Curry recipe below.
Brisket isn't usually a problem unless you don't have enough gravy left. Here are some suggestions if that happens. We have made a very successful second round gravy by browning (long and slowly) an onion or two, thinly sliced, with a clove or two of garlic. You may then add your choice of a cup of chicken broth (don't use beef broth unless it's home made) and season and cook a bit to amalgamate everything, or a 16-oz can of tomato sauce and then include some thyme with the seasoning, again cooking a bit. We have a friend who always cooks extra Prune Tzimmes (and keeps it tucked away) so he can use it as a sauce for the leftover brisket.
I usually just serve roast beef and roast lamb at room temperate, sliced thinly, fat removed, and served with a hot vegetable (a baked potato or a potato gratin is good) and a relish (like a chutney). Again, like the chicken, I don't think they're improved by reheating, unless they're going into a sauce. The only successful reheated roast beef dish I know is an old trick where the roast beef is sliced thinly, and placed in a casserole with a sauce like the onion sauce described in the brisket paragraph above, covered with some buttered crumbs (you can try matzo meal or matzo crumbs if it's still Passover) and heated in a hot oven.
For lamb, I usually create a Kashmiri Lamb Curry. Cube the lamb into 3/4=1" pieces. Chop a large onion. Chop two cloves of garlic and a 1" piece of fresh ginger. Zest a lemon and juice it. Peel an apple and a pear (or two of either) and cut them into small chunks (1/2"). You will also need 1/2 cup of raisins, yellow or black, 2 tablespoons of curry powder (we use Hot Madras, but you may choose a brand and heat of your liking), and 2 tblespoons of potato starch or flour, plus 2 cups of chicken stock and one cup of white wine or vermouth (you may use all chicken stock).
Heat 2 tablespoons of vegetable oil, butter, or margarine in a large saute pan and soften the onion and garlic and ginger. Add the lamb and stir into the onion mixture. Add the apple and pear and soften. Add the flour and curry powder and stir for 30 seconds to blend in the flour. Add the chicken stock and wine and blend in thoroughly, scraping in any brown bits. Add the lemon juice and raisins. Bring to a simmer, lower the heat, and cook for 20 minutes until heated through. Add the lemon zest and serve. (If it's not Passover or you are of the Sephardic tradition, serve with rice.)