In a heavy saucepan cook leek in oil over moderately low heat, stirring occasionally, until softened. Add curry powder and turmeric and cook, stirring, until fragrant, about 30 seconds. Add squash and water and simmer, stirring occasionally, until squash is very tender, about 15 minutes. Cool mixture slightly and in a blender puree in batches until smooth, transferring to a bowl. Season soup with salt and pepper. Chill soup, covered, at least until cold, about 6 hours, and up to 1 day. Before serving, season with salt and pepper if necessary.
Serve soup with small dollops of sour cream and chutney
Recipe courtesy of Gourmet Magazine