Heat the oil in a large saucepan. Add the leek, garlic, parsnip, celery and carrot and stir over medium heat until softened.

Add the potatoes, caraway, salt and stock and bring to a boil. Simmer for 20-25 minutes until all of the vegetables are soft and cooked.

Remove some of the vegetables from the pan and using a stick blender, process the rest until thick and smooth. Return the reserved vegetables and bring back to a simmer.

Remove from the heat and stir in the oregano and yoghurt. Serve.