1 medium onion, finely chopped
500 g Jerusalem artichokes (unpeeled weight)
1 baking potato (ideally around 300 g in weight – definitely not more than this, anyway)
500 g carrots, peeled and sliced
1 or 2 garlic cloves
A generous splash of marsala
1 litre vegetable stock
A few thyme leaves (don’t overdo it)
A squeeze or two of lemon juice
Take a big pan - one that you have a lid for - and soften the onion in it with a spray of oil. If the onion looks like it might take on some colour add a little water. While that’s happening, peel the Jerusalem artichokes as carefully as you can be bothered (as long as they’re clean a little bit of skin won’t really hurt), cut them into chunks and drop them into water with lemon juice added to prevent them going brown.
Peel and cut the potato into chunks. Crush the garlic, stir it into the onions and continue cooking for a minute or so. Add the Jerusalem artichokes, carrots and potato, then pour over the stock and marsala. Sprinkle the thyme leaves over the vegetables. Bring to a simmer, cover and continue cooking until everything is nicely softened – about 25 minutes or so.
Cool a little and then liquidise the lot. Adjust the seasoning and add as much of the lemon juice as you think it needs. Add a little more stock if the soup seems too thick, though don't add too much – I think this soup is best if left fairly thick and creamy (but without any cream, so nice and low in fat).