This bistro has been a favorite with friends and family of mine for years, and as I haven't seen a review of it here, I thought I'd give it a rave. It's kind of a mysteriously undiscussed place... it's not in Zagats and I could find no mention of it on this board.
The restaurant(located on Union St.) is very loosely affiliated with a small French chain of Parisian steak houses (2 branches in Paris and one in Geneva, Switz.), although the SF restaurant is independently owned and operated. It's kind of a quirky place -- they have lounge singers playing there a few nights a week, etc.
Their headliner dish is "l'entrecote" -- sliced steak slathered and dripping in a butter-rich, herbaceously green sauce. Waiters serve generous, never-ending portions of perfect pomme frites to mop up all that sauce. The steak is preceded by a perfect butter lettuce salad (included w/the entree). (There's other stuff on the menu, but I have never tried them because this place is definitely about the steak. And forget the desserts.)
Having become obsessed with this dish, on a recent trip to Paris, I decided to visit the Right Bank outpost (called Relais de l'Entrecote). The place was PACKED with Parisians - throngs were waiting outside for a table on a weeknight. There was no menu -- you're simply asked how you would like your steak cooked. I appreciated the chic presumptuousness of that! To my surprise, I'd have to say that the food at our SF L'entrecote beat the pants off the Parisian version (better meat, more flavorful sauce, just-as-good pomme frites).