He's running a couple of months behind on his timetable, but Napa Valley and New York uber-chef Thomas Keller finally will open his newest restaurant Saturday.

It's Ad Hoc - "for this purpose" - and it will be at the Yountville site most recently occupied by Wine Garden Restaurant, and years ago by the celebrated Diner.

Keller, owner/chef of the Yountville restaurants The French Laundry and Bouchon, as well as Per Se in New York, will operate Ad Hoc only through this winter. Beyond that, he's uncertain what he will do with the property, though he's talked of converting it into a burger joint.

Ad Hoc is to be much more casual than The French Laundry and probably as informal as Bouchon. (Corkage fee at The French Laundry is $50 per bottle; at Ad Hoc it will be $20, unless the wine is on the restaurant's wine list; then guests must buy it from the list.) A blackboard four-course prix-fixe menu will change daily, focusing on comfort foods that Keller enjoyed while growing up, such as fried chicken, beef stroganoff and pot roast. The price is expected to average $45.

(Trivia note: Keller, perhaps the country's most celebrated chef these days, spent part of his time growing up in Sacramento. While his father was stationed at McClellan Air Force Base in the early 1960s, the younger Keller played first base for the Giants, a Little League team in North Highlands.)

At any rate, Keller and his executive chef at Bouchon, Jeffrey Cerciello, will oversee the Ad Hoc menu.

Ad Hoc, 6476 Washington St., Yountville, will not accept reservations, walk-in's only. However, larger parties (10-25 guests) can reserve a space, and the restaurant also is apt to be taken over entirely by big groups (up to 70 people), so it's advisable to call before to confirm that the place is open: (707) 944-2487. Ad Hoc's hours are to be 5-9 p.m. Thursday through Saturday, 5-8 p.m. Sundays.