Cold Cream Of Zucchini And Watercress Soup

Ingredients

• 2 tablespoons unsalted butter
• 1/2 cup chopped yellow onion
• 1 teaspoon minced garlic
• 1 1/4 pounds zucchini, trimmed and chopped
• 1/2 teaspoon salt
• 1/4 teaspoon ground white pepper
• 3 cups chicken stock
• 1 sprig thyme
• 1 cup packed watercress leaves
• 1 tablespoon minced parsley leaves
• 1 cup heavy cream
• 1/4 cup creme fraiche or sour cream
• Watercress sprigs, tough stems removed, garnish
• Chopped chives, garnish
• Cheddar-Pecan Crackers, accompaniment