How long you've been in Houston determines what you remember of the red brick structure on Westheimer in the heart of the Montrose. That funky eatery called Frescos? A '70s club and head shop? Or the original St. Matthews Church? Natives and newcomers alike agree that the current resident, Mark's American Cuisine (1658 Westheimer, 713-523-3800), is the tastiest incarnation of the former church space. And the menu is, well, heavenly. Try the Summerfield Farms lamb loin ($27.95), with a smattering of fresh basil sauce and a gratin of white-cheddar potatoes. These Virginian free-roaming spring lambs are fed corn, wheat and barley as well as grass, which means they have a nice, tasty layer of fat, just enough to make them juicy and tender. The plate of lamb is plenty without being too heavy for these hot days. Baa-appetit!