Our guidebook informed us that despite the rich culinary heritage of France, nothing has ever emanated from Paris except onion soup. Which we did not see on any menus.
Finally on our last day we ventured outside the city to Chartres. And in a wonderful cafe in front of the cathedral we found (and ordered) onion soup. Also a bowl of fish soup with the yellowest rouille I've ever seen. Both were excellent.
If you're in Chartres, go to La Serpente, just outside the southeast door of the cathedral (around to the right from the main entrance). Great food, inexpensive, and you can't beat the view.