Up the waterfall-backed stairs of the W Hotel and through the lobby bar emanating a flattering glow, Nine Thirty has quietly joined the ranks of the city's best restaurants.

Chef Jack Yoss came from San Francisco's Postrio to join Nine Thirty in September 2005, and has been overhauling the menu ever since: The frequent changes reflect his commitment to fresh, seasonal ingredients. On our recent visit just after a menu sprucing, highlights of the small-plates menu included foie gras done five ways, roated butternut squash soup, oysters with American caviar and cilantro mignonette, and grilled tiger shrimp on a bed of nicoise olives, caponata and basil oil. Entres like Kurobuta pork loin and the roasted Sonoma duck breast were tender and intruigingly matched by the young (and female!) sommelier. The late-night menu retains the classy-comfort-food theme with options like a homemade Belgian waffle with fresh berries, Thai-style chicken wings with roasted peanuts and waffle fries, and a toasted brioche sandwich with Black Forest ham and cheddar. Amid the bamboo-screen walls and mixture of woods light and dark, classy execs and pretty young things enjoyed Yoss' cuisine on our visit, a crowd to be expected at a restaurant from the owners of Tengu, Holly's East, Holly's West, Venice Cantina and Nacional.

October 16 marked the beginning of "Mushroom Mondays," on which chef Yoss celebrates the fall season with a special menu of small plates in the fungi family. Examples from the ever-changing menu include mushroom mac n' cheese with Boschetto Al Tartufo (it's a cheese; "al tartufo" means with truffles), wild mushroom soup with black truffle-foie gras emulsion, or pan-roasted hen-of-the-woods mushrooms and crme frache atop grilled sourdough toast with truffle oil. The plates cost $12 to $16 each.