Leftover casserole keeps well in the refrigerator for up to 3 days. Allow it to cool completely, then cover tightly with plastic wrap or transfer to an airtight container. To reheat, place individual portions on a microwave-safe plate and heat for 1–2 minutes until hot, or rewarm the whole dish in a 325°F (165°C) oven, covered, for 15–20 minutes.