In a large saucepan, heat the oil and add the carrots and cook gently for a few minutes.
Add the water or stock, bring to a boil, cover, reduce the heat and simmer for 15 minutes.
Using a blender, liquidize the carrots and cooking liquid with the coriander, reserving a few leaves for the garnish. Season to taste. Garnish each serving with a swirl of sour cream