Fill a large plastic container with 1 litre (35 fl oz/4 cups) water and add the citric acid. Peel the salsify and place in the acidulated water — this will keep them from discolouring. Place the onion, carrot, celery, garlic, bay leaf, thyme, peppercorns, wine, vinegar and lemon peel with 325 ml (11 fl oz) water in a large saucepan and bring to the boil. Drain the salsify, add to the pan, return to the boil, then reduce the heat to low and simmer for 10 minutes. Remove from the heat and allow the salsify to cool in the stock. Cut the salsify into small pieces and set aside.
Quarter the pine mushrooms, place in a saucepan over medium heat with the oil and cook for 2–3 minutes. Add the leeks and cook for 1 minute. Set aside and keep warm.