Anyone who has zucchini in their garden understands the importance of having numerous recipes that call for this prolific producer. Soup is easy, it freezes well, and this concoction tastes great hot or cold. Vegetable stock can be substituted for the chicken stock if you wish.
If the zucchini are small, slice into 1/4-inch thick rounds. If they're large, cut each squash in half lengthwise, and then slice crosswise into 1/4-inch-thick pieces. Set aside.
Heat the butter in a large saucepan or stockpot over medium heat. Add the leeks and cook, stirring frequently, until soft and tender, about 8 minutes. Add the garlic and curry powder, and cook for 2 minutes, stirring frequently. Add the chicken stock and the sliced zucchini, and bring the soup to a boil over high heat.
Reduce the heat to medium, cover the pan, and cook until the zucchini is tender, about 15 minutes. Uncover and let the soup cool slightly. Purée in a blender, food processor or with an immersion blender.
If you plan to serve the soup hot, reheat over low heat. Season to taste with salt and pepper, then divide the soup among warm bowls. Drizzle each serving with some crème fraîche, if using.
To serve cold, cover and refrigerate the puréed soup until thoroughly chilled. Garnish with crème fraîche, if desired.