Put casserole together and freeze it before baking. When you’re ready to cook it, let it thaw in the fridge over night. If it’s still slightly frozen in the middle, you’ll just have to cook it longer than the recipe calls for or defrost a bit in the microwave before baking. Cover it with foil if the top gets too brown in the oven. Bake for about 20-25 minutes or until golden on top and bubbling on the sides.