This jewel in Rick Bayless' crown welcomes a rush of diners for original Mexican food with an upscale twist. While you have to walk through cacophonous Frontera Grill to get here, the serenity that greets you is well worth it. The menu, boasting a panoply of flavors and textures, spins with the seasons all the while highlighting regional cuisines and holidays. Though each dish is rooted in tradition, there's no shortage of flair, as in kampachi sashimi decked with the flavors of street corn. There's also a canon of sauces treated with appropriate reverence. To wit, Oaxacan mole chichilo is a symphony of dried chiles, nuts and spices, and makes a sublime counterpoint to lamb loin.Drinks are noteworthy, but teetotalers will relish those agua frescas.