Baked Umbrian Cardoons

This dish is rather like a layered lasagne but uses cardoons instead of pasta. It is a great pity that this delicious winter/spring vegetable (the stems of the plant are eaten) is not grown more extensively in the UK: it is enjoyed all over Umbria, the Abruzzi and Lazio. If you have never seen or cannot get cardoons, thick celery - as white as you can find - is the only possible substitute. Serve as a lunch or supper dish with a salad and plenty of crusty bread.