After the casserole is baked, you can store any leftovers in the fridge for 3 - 4 days, tightly covered. For best flavor and texture, however, I like to eat leftovers within 2 days. You can even bake the casserole, let it cool for about 15 minutes, and then cover and place the entire thing in the fridge. When you're ready to serve, cover the top of the casserole with aluminum foil, then heat in a 350 degree oven for 25 - 30 minutes until heated through and bubbly. (But, to avoid thermal shock which could damage some types of glass or ceramic casserole dishes, let the casserole dish warm to around room temp first before placing in the preheated oven.)