Heat the oil in a large pan, add the onions, carrots. and garlic. Sauté for 4 minutes until they are beginning to soften but not color. Stir in the ground coriander and plenty of seasoning and cook for 1 minute.
Add the stock and bring to a boil, then cover and simmer for 20 minutes or until the carrots are really tender. Stir in the fresh coriander.
Whizz the soup with a stick blender or transfer to a food processor. Add the lemon juice and nutmeg to taste and adjust the seasoning as necessary. Reheat until just hot but not boiling and serve. Garnish with a swirl of cream if desired.