1 large onion, halved and sliced
675g/1½lb Jerusalem artichokes, peeled, halved and sliced
2 tbsp extra virgin olive oil
4 sprigs fresh thyme
1 bay leaf
1 litre/1¾ pints hot chicken or vegetable stock
2 tbsp white wine vinegar
salt and freshly ground black pepper
2 tbsp roughly chopped parsley
6 thick slices baguette (optional)
150g/5oz single Gloucester, mature cheddar or gruyère cheese, coarsely grated (optional)
1. Place the onion, artichokes and oil into a pan and add the thyme and bay leaf, tied together with string. Cover and sweat over a low heat for about 15 minutes, stirring occasionally.
2. Add the stock and vinegar, season well with salt and freshly ground black pepper and bring up to the boil. Simmer for ten minutes, then taste and adjust the seasoning. Discard the thyme and bay leaf and pour into serving bowls.
3. To serve, sprinkle with parsley. If using the bread and cheese, preheat the grill to medium. Toast the baguette lightly on both sides under the grill, then, just before serving, top with grated cheese and slide back under the grill to melt. Float a slice of cheese on toast in each bowl of soup as you serve.