French black truffles are most definitely not a supermarket item, and I have therefore made their use optional. Truffles are fungi that grow underground and are prized for their unique flavor. They can range in size from ½ inch in diameter to as large as 2 to 3 inches, and in their fresh form are usually found only in a few high-end specialty stores and expensive restaurants. I call for medium-size truffles, which measure about ¾ inch in diameter, packed in cans or jars.