Au Cheval
A sister restaurant to Bavette’s, Au Cheval is home to Chicago's best burger. Just remember that the single is really a double and that the double is really a triple, and to always add the bacon. Au Cheval is a dimly lit diner with a speakeasy vibe and a menu full of rich foods. A prime example: The fries drown in Mornay sauce topped with a fried egg. Expect a long wait (up to four hours) before you get to eat, but you can pass the time in the bar next door. If you want to skip the long line, try arriving 15 minutes before they open for brunch, and yes, the burger is on the brunch menu.
See the Blog Post: http://thekittchen.com/au-cheval-best-burger-chicago