Vichyssoise

Cut off roots and trim dark green tops from leeks; cut each leek lengthwise in half. Cut enough of white and pale green parts crosswise into 1⁄4-inch pieces to equal 4 1⁄2 cups. (Reserve any leftover leeks for another use.) Rinse leeks in large bowl of cold water, swishing to remove sand; transfer to colander to drain, leaving sand in bottom of bowl. In 4-quart saucepan, melt butter over medium heat; add leeks and cook, stirring occasionally, 8 to 10 minutes. Add potatoes, broth, water, salt, and pepper; heat to boiling over high heat. Reduce heat; cover and simmer 30 minutes. Spoon half of mixture into blender; cover, with center part of cover removed to let steam escape, and puree until smooth. Pour into bowl. Repeat with remaining mixture. Stir milk and cream into puree. To serve hot, return soup to same clean saucepan and heat through over low heat (do not boil). To serve cold, cover and refrigerate at least 4 hours or until very cold. Makes about 8 cups or 8 first-course servings. Nutritional information is based on one serving.