While the original hamburger may have its origins in Germany, nothing is more American than the modern day hamburger. There are several claims to who really invented the modern hamburger so I'll leave that discussion to the experts. If you'd like to learn more about the history of the hamburger, read more on Wiki.
Now if you want to know where to get the best hamburger, you'll find no better burger than the one served at Washington Square Tavern in Brookline, Massachusetts. A 1/2-pound behemuth served with crispy fries and the Tavern's "Moon Brine" pickle, a decidedly sour spear. Cheese it if you will, but this burger is cooked to perfection and delicious no matter how you top it.
In addition to their savory sandwich, Washington Square Tavern also serves superb steaks, seafood, and salads. Everything is excellent. Owner Gerry meticulously selects the wine list and has an outstanding reserve offering. You'll also find dinner and wine specials on the menu. Washington Square Tavern does not take reservations though, so be prepared to wait if you go during dinner hours.
Authors note: I removed the description of WST calling it an American bistro.