If you are having a big party, here are some recipe suggestions that might help out. We use to cook meals at church for groups of 40-80 and these were great. I have some of them listed here, or you can search for "Crowd Pleasers".
If you want to do a big casserole for 30-40, I recommend buying disposable counter pans. They can be found at Sams, Costco, or most party stores. They are sometimes called Steam Table Pans and are 21x13x3 in size. I recommend you use two pans so that they are easier to get in and out of the oven. You could also put them on a large cookie sheet for support. They are made of aluminum and because of all the folds and creases, they are single use pans. If you use two pans for support, you can re-use the outside pan, but there is just no way to insure the inside pan is completely clean. I have this from our resident food safety expert, so don't feel bad about throwing that pan away!!
But if quantity cookery isn't your thing, you may find that you don't have much need for a recipe that will feed 40 at a time... or do you??
Here's the thing about Quantity Cooking... It's not just for parties. If you have a freezer, several of these recipes will allow you to separate the recipe into family size servings and freeze for future use. I have tried to note it when that will work with the recipe. Look for "Freezer Favorites".Â