There are three keys to making a superb cheese steak. First, shave the beef until you can see through it. Then ensure that the onions and peppers are well caramelized and the mozzarella well melted. And finally, slather it all onto a crusty roll. The folks at Market Square Bar and Grill (311 Travis, 713-224-6133) not only understand the basics, but they add some delightful twists to the classic sandwich ($7.95). Mixing blue cheese with the mozzarella gives it an unexpected tartness. Jalapeños and a dipping sauce of horseradish, cayenne and mayonnaise adapt the Philadelphia dish to local taste buds. But as good as Market Square's cheese steak is, only the in crowd knows to order it. It's an off-the-menu special.