Potato and Leek Soup with Yoghurt

Cook the potatoes, celery and leeks in the water in a tightly covered saucepan. Press through a sieve.

Combine the sieved vegetables with the milk and yoghurt in the top part of a double boiler. Stir in the salt, celery salt and pepper. Heat over boiling water for fifteen minutes, stirring occasionally. Sprinkle each serving with chives.