Cucumber Vichyssoise

5 cups chicken stock
3 cups peeled and sliced potatoes
2 tb butter
3 cups sliced white of leeks
1 small onion sliced
1 large cucumber, peeled, seeded and sliced
1 1/2 cups heavy cream
1/4 tsp nutmeg
salt and white pepper
3 tb minced chives

Pour stock into a large saucepan, add potatoes, bring liquid to the boil, reduce heat, cover and simmer for 20 minutes or until tender. Heat butter in a skillet, add leeks and onion, and sauté over low heat for 5 minutes. In batches, combine vegetables and stock in the processor, add cucumbers and puree. Pour mixture into large bowl. Stir in cream, add nutmeg and salt and pepper, stir and chill thoroughly. Serve in chilled soup bowls and garnish with minced chives.