Peel and dice the celeriac. Slice the leek then chop the garlic. Thinly slice celery and put the leaves aside.
Heat the oil a large saucepan and gently sauté the leek & celery over a low heat for 8 minutes or until softened.
Add the celeriac and caraway seeds, then stir for a minute or so.
Add the stock, bring to the boil, then simmer for about 20 minutes.
Using a hand-held blender, process the soup with until it’s smooth and silky. Add more stock if it’s too thick. Season to taste.
Stir in the apple cider vinegar or sour cream and serve warm with the celery leaves .