the entire nightshade family - tomato/potato/etc - along with maize - is New World. food focused on those would be by definition "American (continent)" stuff.
stellar example: cornbread/pudding, grits, polenta.....
other things that come to mind:
fruit pies - a bottom/top crust baked dish is common throughout Europe, but not with fruits. 'American as apple pie' has a lot of truth to it.
corned beef - corned meats in merrie ole England were pork/lamb/mutton. the Jewish deli's in NYC would of course not handle pork, so they 'invented' the beef variant to make the later Irish immigrants happy.
pizza. [[[stand-by, large caliber incoming . . . ]]] the older tomato pie of course could not exist before the New World. dough with toppings existed salotta' places.
I would posit the American style everything including the kitchen sink is indeed 'American' - the overboard toppings are simply not found in Italy/Europe - until much more recently, as it the 1990 and later....