REMOVE THE ROOT END OF THE leeks, trim the dark green tops and reserve foranother use. Slice the light part into 1 cm rounds, wash well and setaside on a plate.
Heat the oil in a pot, over medium heat, and add theleeks. Cook, stirring, for 5 minutes. Add stock, water, potatoes, nutmeg,salt and pepper. Raise heat to high, cover and bring to a boil. Reduce heatto low and simmer, uncovered, for 30 minutes.
Remove from heat and pureethe soup in batches. Place pureed soup in a pot and reheat, covered, overlow heat. To serve, place a generous dollop of sour cream in the bottom ofeach soup bowl and sprinkle with chopped chives. Transfer piping hot soupto a tureen or pitcher and pour into bowls at the table.
Refrigerate soup for up to 3 days or freeze the soup.