1. 取出一個大小洽當的煮食鍋，用橄欖油把洋蔥略炒 5 分鐘至半透明和軟身。用繩將百里香綁起來，跟根芹菜、薯仔和雞湯加到鍋裡去。
In an appropriately sized pot, slowly fry the onion in the olive oil for about 5 minutes until translucent and soft but not coloured at all. Get your bunch of thyme, tie it up with a little string and add to the pot with the celeriac, potatoes and stock.
2. 煮至沸騰後再炆煮 40 分鐘，直到蔬菜變軟身。加入奶油煮至沸騰，然後取出百里香，其他的倒入食物處理器攪拌。
Bring to the boil and simmer for 40 minutes until the vegetables are tender. Add the cream, bring back to the boil, then remove the thyme and purée the mixture in a liquidizer or food processor.
3. 試味，要一匙接一匙的添加松露油 — 不同品牌的松露油味道不一。
Season carefully to taste, adding the truffle oil tablespoon by tablespoon – the oil can vary in strength depending on the brand.
Divide between your serving bowls. Feel free to improvise by adding croûtons, a little extra cream or, if you’re really lucky, some real black or white truffles shaved over the top.
5. 試試這個： 飲用前撒上一些切碎的香菜、芹菜葉、少許橄欖油和檸檬汁。
Try this: If you want to give an edge to this comforting soup, try dressing some chopped parsley and celery leaves with a little olive oil and lemon juice. Sprinkle over the soup at the last minute before serving.