I think we'd be pretty hard-pressed to come up with something that isn't originally from someplace else. All we can really go for is "American preparation of [x dish]" 
For example, the iconic image of American meatloaf involves a ketchup-based sauce baked on top. Although frankfurters aren't native to the USA, a Chicago dog, with all the fixins, could reasonably be considered an American institution.
This is pretty much the point I was trying to make, although too obscurely. Many dishes may be typically American but are most certainly not exclusively American. The trick is to find what -- if anything -- makes them unique.
One other problem is finding ingredients here in Europe. Molasses? Cranberry sauce? Don't exist here. Pecans? Yes, at Christmas and barely affordable.
One of our most successful parties was an "American-style cookout" with hamburgers and cheeseburgers, chicken breasts, baked beans and watermelon. All commonly available foods here in Germany, but perhaps not so commonly eaten (the baked beans) or prepared in different ways.
And a brownie trifle for dessert!
