If you are making this casserole the day before for convenience, you have two good options. You can bake it immediately and reheat the next day in the oven, or cover the uncooked casserole with foil and refrigerate overnight (You can actually cover and refrigerate for up to two days before baking). We recommend that if you choose to refrigerate overnight you take it out of the refrigerator 30 minutes before reheating or baking.