The unbaked muffin batter will keep for up to 2 weeks in the refrigerator in an airtight container. You can bake muffins fresh daily or at any time by baking the desired quantity at the last moment. You can also bake and freeze them. Just thaw in the microwave for mornings in a hurry or bake at 180 °C (350 °F) for about 15 minutes to get a crunchy muffin top.