rue lepic, corner of pine and mason
the food is amazing, the kitchen is in the front so you see them making everything fresh (just one chef, the female owner) and the waiter is super nice.
it's tiny, quaint and really freaking amazing. i think they're only open for dinner. with a date get the prix fixe and an entree and share the salad, appetizer and desert with your date.
counting the atmosphere, quality of service, amazing quality of food, portion size (it's not one of those uppity here's two peas and a carrot restaurants) it's simply the best restaurant i have ever eaten at in san francisco or new york. it's hardly reviewed or advertised anywhere because the people who eat there want to keep it for themselves.