Creamy Mirliton Soup

3 tablespoons butter
2 medium-large mirlitons (about 1½ pounds), quartered, peeled, pitted, then each quarter thinly sliced
1 large Vidalia onion (about ¾ pound), halved, peeled, then each half thinly sliced
1 medium celery rib, trimmed and thinly sliced
3 large parsley branches
1 large whole bay leaf, preferably fresh
3 cups chicken broth
½ teaspoon salt, or to taste
¼ teaspoon black pepper, or to taste
1 cup half-and-half
¼ cup buttermilk
2 tablespoons finely snipped fresh chives

Also called chayotes, vegetable pears, or custard marrows, mirlitons are particularly popular in the Deep South where they are grown commercially.

Melt the butter in a large, heavy saucepan over moderately high heat; add the mirlitons, onion, celery, parsley, and bay leaf and stirfry for 2 minutes. Reduce the heat to moderately low, cover, and cook, stirring occasionally, for 20 minutes or until the vegetables are golden.
Add the broth, salt, and pepper and bring to a boil over high heat. Adjust the heat so the soup bubbles gently, cover, and cook for 50 to 55 minutes or until the vegetables are soft.
Pour all into a large fine sieve set over a large heatproof bowl; discard the parsley and bay leaf. Purée the solids in a food processor or electric blender at high speed.
Combine the puréed vegetables with the soup liquid, then mix in the half-and-half and buttermilk. Taste for salt and pepper and adjust as needed. Cover and chill overnight.
Either serve cold, garnishing each portion with the snipped chives, or reheat just until the mixture steams; do not boil or the soup may curdle. Ladle into heated soup bowls and sprinkle each portion with the chives.