Info: from The Old Farmer's Almanac Colonial Cookbook Wash the sorrel leaves and cook them in the butter until just wilted. Puree' the sorrel and add other ingredients, dissolving the cornstarch first in a little stock, or whirl all together in the blender. Then cook the soup over gentle heat until slightly thickened. Serve hot or chilled, garnished with sour cream and chives, or with thin slices of lemon. Courtesy of Fred Peters.