Best French Onion Soup
You might want to try our various French bistros, most of which will have the soup on the menu. There's a comprehensive list of them, with links to their websites, at http://chowhound.chow.com/topics/602957
Bistro Bordeaux in Evanston has both items on their regular menu. Last time I went to La Sardine they had foie gras as a daily special.
Today I had lunch at Barrington Country Bistro in northwest suburban Barrington. They change their menu daily, and the up-to-date menu appears on their website.
They had French onion soup and I got the impression this is one of their signature dishes and almost always appears on the menu. I did not try it but my dining companion did and pronounced it outstanding; it was redolent of raclette. They did not have foie gras on their lunch menu but it appears on tonight's dinner menu. www.barringtoncountrybistro.com
Barrington Country Bistro
700 W Northwest Hwy, Barrington, IL 60010