Heat the oil in a large saucepan over medium heat.
Add onion and saute until softened, about 3 - 4 minutes.
Add the carrots, potatoes, celery, coriander, parsley, and garlic. Pour in the vegetable stock and simmer over low heat until the carrots and potatoes are tender, about 20 - 30 minutes.
Remove from the heat and puree with your stick blender.
Return to the heat and season with salt and pepper to taste. Simmer over low heat till ready to serve.
Ladle into soup bowls and garnish with yoghurt and celery leaves.