Chop the leeks, carrots, courgettes and pak choi stems
Stir fry for about 3 minutes. Add the buckwheat and keep stirring for another 3 minutes.
Add salt, turmeric, coriander and soy sauce and stir for about a minute. If you are using fresh coriander keep it to add at the end, when the soup is cooked.
Add boiling water and cook until the buckwheat softens.
At the end add the pak choi leaves, roughly chopped and cook for another 3 to 5 minutes