Separate the tarragon stalks from the leaves, reserving the leaves to finish the soup.
Peel the carrots, onions and celery and roughly chop. Thinly slice the leeks and the fennel. Cover with water and add the tarragon stalks and the coriander seeds. Bring to the boil and then reduce to a simmer. Simmer for atleast 40 minutes and then pass the liquid through a sieve.
To make the bouquet garni use the green part of the leek atleast 10cm long. Place the stick of celery with the thyme and parsley stalks in side. Wrap the leek over to enclose the herbs and then tie with string.
Peel the onion, carrot and celery.
Brunoise the onion and carrot. This is cutting them into fine dice.
Peel the garlic clove and puree the flat of your knife with a pinch of salt.
Cut the fennel in half, remove the tough core and then cut into diamonds.
Cut the potato into batons and then into small dice.
Cut the celery into thin slices at an angle.
Cut the leeks into very thin strips or julienne.
Pick the parsley and tarragon leaves and then shred carefully. This technique is called chiffonade.
Zest and juice the lemon.
In a heavy bottomed pan start by sweating the onions, fennel and garlic in a splash of olive oil. Sweating is to slowly cook without colouring. Season with salt and pepper.
After 5 minutes add the celery, potato and carrots and continue to cook for a further 5 minutes. Cover with the stock and add the bouquet garni. Cook for about 10 minutes or until the potato is soft. Remove from the heat and whisk in the butter. Add the chopped herbs, a pinch of lemon zest and a squeeze of juice.
Meanwhile heat a fryer or a saucepan with sunflower oil to 180'C. Deep fry the leeks until crispy. Remove from the fryer and drain on kitchen paper. Season with salt.
Serve the soup with the crispy leeks on top.
«Always add soft herbs like tarragon and parsley just before serving. Cooking the leaves too early will ruin their delicate flavour and cause them to discolour.»