Shepherd's pie was originally made with lamb or mutton; it was invented as a way to use leftovers from the Sunday roast. When the dish is made with beef, it's actually called cottage pie, but we'll just have to make some allowances for the sirloin shepherd's pie ($9.95) at Brian O'Neill's Traditional Irish Pub (5555 Morningside, 713-522-2603). Theirs is such an outstanding rendition of the classic, it doesn't matter what they call it. Large chunks of stout-marinated, slowly braised sirloin steak commingle with ground beef in the thick gravy. The all-in-one dish includes carrots, peas, leeks, onions and a substantial layer of mashed potatoes that covers the entire dish and is perfect for sopping up the gravy. A little thyme and black pepper are the only seasonings needed.