Melt the butter in a large saucepan, add the leek, onion, celery and garlic and cook over low-medium heat for 5 minutes or until vegetables are tender but not coloured.
Add the potatoes, cover and cook for 10 minutes, then add enough stock to cover. Cook, covered, for 15 minutes or until potatoes are tender.
Purée soup in a blender until smooth, then pass through a fine sieve into a large saucepan and re-heat over low heat until warmed. Add the crème Fraîche and stir to combine, and then season to taste with sea salt and freshly ground white pepper.
Heat lemon oil in a frying pan, add the washed and still wet Swiss Chard and cook until just wilted. Divide Swiss
Chard among serving dishes, ladle over soup and serve immediately, drizzled with a little extra lemon oil, and crusty bread served separately.Recipe reprinted with permission of Potatoes South Africa with Arnold Tanzer.