Cut the leek in half lengthwise, then slice into 1cm pieces.
In a large saucepan heat the oil and soften the leek at low temperature.
Meanwhile, peel the potatoes (not necessary, if organic) and cut into bite-sized pieces. Slice the chicken thinly or into bite-sized pieces.
When the leek is soft, add the garlic and the potato cubes and cook for 3-4 minutes.
Add the chicken, star anise and pour in both stocks. Bring the soup to the boil, then simmer, under cover, for 20 minutes (at low heat).
Slice the sage leaves into thin strips, peel & grate the ginger.
When the meat and potatoes are cooked through, take the soup off the stove and add the sage & ginger. Put the lid on and rest for a couple of minutes then serve.