Of all the culinary accidents in human history, which include the chocolate chip cookie and, if you believe Charles Lamb's account, roast pork -- surely fudge must rank among the most serendipitous. No one knows for sure just who made the first pan of fudge, but most everybody agrees it was invented by mistake -- and it's uniquely American. As Lee Edwards Benning notes in her exhaustive treatise on the subject, fudge was unknown outside this country by those who might've been expected to