Put the oil into a large saucepan, add the onion and garlic and cook over a very low heat, covered, for 10 minutes, making sure the onion does not brown.
Peel and chop the apple, parsnip and potato. Add the apple and parsnips to the pan and cook for a further 5 min.
Add the wine, bring to the boil and reduce by half, then pour in the stock and add the potato. Season carefully with salt and pepper.
Bring to the boil, then lower the heat and simmer gently for about 20 min or until the vegetables are soft.
Puree the soup with a blender and add enough milk to achieve the consistency of thick cream. Adjust the seasoning to taste and stir in the creme fraiche.
Serve hot with a garnish of chives.