Gently cook the onion in the ghee for around 3 minutes, then add the carrots and parsnips and saute for a further 10 minutes.
Add the stock or water, bring to the boil and simmer for about 10-15 mins, until the vegetables are soft.
Blend the soup (this is best done with a hand blender directly in the pan, but if you don’t have one simply transfer to a blender and then return to the pan).
Add in the lentils and cumin and cook again for another 10-15 mins, until the lentils are soft.