German chocolate cake is a winner! it is a truly American food.
General Tso's chicken is just an "Americanized" Hunun "commoner" dish. It was originally made without the sugar which was added to the ancient food for Americans.
Smores were originally made in mid 19th century Russia.
It is widely thought that fortune cookies are an American original but Fortune Cookies Were Invented in Japan. After World War II, it is well documented that fortune cookies were almost exclusively being served in Chinese restaurants in California.
While Corn Dogs were first used in the US in the 1940's the act of deep frying sausages with batter was used in Egypt when the Pharaohs ruled if not before. The Hot dog is a sausage made of pork, beef, chicken, turkey or some combination of those meats - not typically American in origin. Corn is, or was, a wholly American grain so dipping the sausage in corn batter is new but the overall food has just been Americanized.
Milk shake? The term ‘milkshake’ was first mentioned in a British newspaper in the year 1885. The drink was described as a “sturdy, healthful eggnog type of drink, with eggs, whiskey, etc., served as a tonic as well as a treat”. When ice cream or ice milk was used it was called a "thick shake".
English muffins, or breakfast muffins as they are known in their origin the United Kingdom, are a small, round, flat yeast-leavened bread which is commonly sliced horizontally, toasted, and buttered.
The term "English Muffin" is the only American part of the food.
Another "American" food has to be Cornbread. Mankind has been making bread since they started grinding grain but corn is a truly American grain so it is an Americanized food and not truly American.
So we have one truly American food so far thanks to Sentry.
I can add one more American food: Tortillas! While flat breads are not native to the Americas the tortilla is less complex and has its origins in America. There are a host of other Mexican foods that are truly American although not attributable to the United States.
We could also add pemmican to American foods and there are probably more American Indian foods as well.