4 leeks, welled washed and chopped
1 onion, chopped
1 tablespoon butter
2 potatoes, peeled and chopped
1 cup water
2 teaspoons salt
2 cups milk
2 cups half-and-half
1 cup heavy cream
1 teaspoon white pepper
In a kettle, cook chopped leeks and chopped onion in butter over low heat, stirring occasionally, until softened. Add peeled, chopped potatoes, water, and salt. Simmer the mixture, covered, for 30 to 40 minutes, or until the potatoes are soft. Add milk and half-and-half. Bring the mixture just to a boil, stirring.
Allow to cool. In a food processor, puree the mixture in batches and strain through a very fine sieve into a bowl. Stir in cream and white pepper. Chill, covered, until cold.