Cooking a holiday meal is a bustle of activity, and you’ll often need to have several dishes ready to serve at the same time. To make the preparation easier, some dishes can be made ahead and cooked or heated before serving, and this casserole is one of them. To make it ahead of time, follow most of the steps of the recipe and stop after you pour the mixture into an oiled baking dish (just leave out the step about preheating the oven). After you pour the hot casserole mixture into the dish, let it cool to room temperature, cover with foil, and refrigerate.
Don’t freeze the casserole because the ingredients don’t hold up well to freezing. The dish will become watery with an off texture. Although this recipe doesn’t call for it, some people like to stir some of the fried onions into the sauce. We don’t recommend doing that when making this ahead because the crisp onions will get soggy. Before you’re ready to serve it, take the dish out of the fridge and let it come to room temperature for about 30 minutes. Then, all you need to do is preheat the oven, top the dish with fried onions, and bake it for 15 minutes, until it’s hot and bubbly and the onions are nicely browned.