Store in the refrigerator in an airtight container for 5-7 days.
This caramel reheats beautifully in the microwave or stovetop.
You can also freeze the sauce for up to 3 months. Just make sure to use an airtight container that's NOT glass because the milk expands when frozen and can rupture the glass. Defrost the sauce overnight in the fridge and warm gently before using.