Place the potatoes, carrots and stock in a saucepan and simmer 20 minutes, until the vegetables are soft.
Meanwhile, cut the zucchini into quarters lengthwise and then cut into thin slices. Halve the leek and also cut into thin slices. Heat the oil in a saucepan and saute the zucchini, leek and chilli until soft. Season with salt and pepper.
Puree the potato and carrot mixture and season with salt, pepper and nutmeg to taste.
Stir in the sauteed zucchini and leeks, serve up the soup and top with a dollop of sour cream.