Purée of Spring Vegetable Soup

Procedure

1. Heat the butter in a heavy soup pot over low heat.
2. Add the leeks, potatoes, and celery. Sweat over low heat until fairly tender, about 10–15 minutes.
3. Add the peas, parsley, and tarragon. Sweat another 5 minutes.
4. Add the stock. Simmer 10 minutes or more, until the vegetables are tender but not overcooked.
5. Purée t