This flavoursome purée of the inexpensive root couldn't be simpler and is delicious as an accompanying vegetable with lamb, pork or duck. Don't forget to save some of the cooking water for adding to the purée. The purée can be prepared ahead of time and reheated later, in which case a little more of the cooking water can be added if necessary, but do not add the olive oil and Parmesan until the very last minute.
Serve each tart with cream on top and the sauce on the side.
Allow to cool slightly before serving.