Onion For Potato Gratin

Our answer

Nigella's Creamy Potato Gratin (from NIGELLA BITES) simmers thinly sliced potatoes in milk and cream until tender, before transferring them to a baking dish to finish off in the oven.

A whole, peeled onion is added to the milk mixture to add extra flavour, similar to the way an onion flavours the milk for a bechamel sauce. We would normally remove the onion before transferring the mixture to the baking dish. The onion could be discarded or refrigerated for up to 5 days and cut up and used in another recipe, such as a tortilla, but if you prefer to slice or chop the onion and include it in the finished gratin then that is fine too.