Heat the oil in a large pan and add the onion, saute for about 10 minutes until soft. Stir in the garlic and ground coriander and cook for another 2 minutes.
Add the carrots, potato and vegetable stock. Bring up to the boil then turn down to a simmer and cook for about 25 minutes until the carrots and potato are soft.
Remove from the heat and add the milk and coriander. Use a stick blender to blend the soup until smooth. Season to taste with salt and pepper and serve.