They look like black olives, but they are whole walnuts, picked green in the Ararat Valley of Armenia, and steeped in sugar syrup until they turn lush, sweet, tender and irresistible, a little like marrons glacés, only moister. They are made by Harvest Song, a company that specializes in excellent Armenian preserves. The walnuts are a perfect foil for pungent cheeses, pâté or roast duck or game. You can also nibble them after dinner or slice them to decorate pumpkin pie. And that manhattan? Drop a preserved walnut in the glass instead of a maraschino cherry.