Heat the oil in a large nonstick pan and add the onion, garlic, celery, carrots, parsnips and thyme. Cover with a lid and cook gently for 15 mins, stirring occasionally, until the onions are softened and beginning to colour. Add the rice and pour in the stock. Bring to the boil, then reduce the heat to a simmer and cook, uncovered, for 15 mins, stirring occasionally.

Season to taste with salt and freshly ground black pepper, then stir in the leeks. Return to a gentle simmer and cook for a further 5 mins or until the leeks have softened. Adjust the seasoning to taste and blitz half the soup with a stick blender, leaving the other half chunky, if you like. Top with the parsley and serve in deep bowls.