This is a lovely, thick soup that’s rich and full of flavour and utterly redolent of autumn. It’s also very good eaten with toasted bacon sandwiches, in which case it’s a meal in itself.
Melt the butter in a heavy-based pan and sweat the celery and onion together, covered, on a very low heat, for 30 minutes, stirring occasionally. Add the leek and potatoes and cook for a further 15 minutes. Add the stock, celery seeds, a pinch of celery salt and a generous grinding of pepper. Bring the soup to the boil and simmer for 20 minutes.