Chef Louis Diat created this classic soup in the early 1900s, while working at New York's Ritz-Carlton hotel.
- 4 Tbsp. butter
- 4 leeks, white and light green parts only, thinly sliced
- 1 medium onion, thinly sliced
- 5 medium white boiling potatoes (about 2 1⁄4 pounds), peeled and thinly sliced
- 2 cups milk
- 2 cups light cream
- 1 cup heavy cream
- 2 Tbsp. finely chopped chives
Heat butter in a large pot over medium-low heat. Add leeks and onions and cook, stirring occasionally, until soft but not browned, about 20 minutes. Add potatoes, 4 cups water, and salt to taste and increase heat to high. Bring to a boil, reduce heat to medium-low, and simmer, stirring occasionally, until potatoes are soft, 50–60 minutes.
Strain soup through a mesh sieve into a bowl, pressing and scraping the solids with a spoon. Clean pot and return soup to it. Whisk in milk and light cream, bring to a boil over high heat, then remove from heat and let cool. Strain soup through a fine-mesh sieve (finer than the first), pressing and scraping it into a bowl with the spoon, leaving behind a thick paste of solids. Discard solids. Stir heavy cream into soup, cover with plastic wrap, and refrigerate until chilled. Season soup with salt to taste.
Divide soup between 8 soup bowls and garnish with chives. Serve cold.