I have never bought the “The best(or real) pizza is only found in Italy” Or “The only real Chinese food in only found in China” or any similar notion.
People who say these things are pretty adamant about it.
If Mom and Pop came from the olde country and opened a pizzaria (or Chinese,or French, Mexican,Indian,whatever) restaurant. And also brought the olde recipes, cooking techniques,etc,etc.
I ask you,The Dope,why wouldn’t the food be ‘authentic’?
It is very hard to find Chinese food that is authentic here. When I lived in China, I was shocked how much better(and different) the food was.
Chinese people told me that the oils and spices are not available very easily in America.
Having said that, I’m sure that you can find genuine Chinese food here. It’s just not the common stuff you get at a run-of-the-mill Chinese restaurant.
I’m sure New York Dopers (and expatriates) alone can supply several fill-in-the-blanks for “the best _______ is only found in New York.” It’s almost an article of faith here.
When I lived in Chicago I grew really weary of the New York vs. Chicago pizza-by-the-slice wars. This rivalry tends to get carried over into hot dogs as well. I don’t care. A hot dog without ketchup is a total deal breaker.
The best Bar-B-Que is only found in North Carolina. Don’t even bother arguing with me. 
Before the Catsup Castigation Corps arrives to behead you, allow me to throw in my agreement.
The best poutine, if you ask me, is found in northern Québec. Restaurants in New York, and even in certain touristy parts of Montreal, tend to use bagged shredded cheese instead of real curds…and while fries with cheese n’ gravy can be yummy, when I order poutine, I want poutine, dammit.
I wish I remembered the name of the place I had it in Old Quebec. They made their own with hand-cut fried potatoes, fresh curds, and a chicken gravy homemade from the rotisserie drippings. Mmmmmmmmmm.
That’s really the only food I’ve had for which I haven’t found a reasonable approximation elsewhere. Perhaps I’ve just been lucky?
I so know what I’m having tonight. 
Moved from IMHO to CS.
NYC expatriate here.
Kosher deli
Pizza
Chinese/American
Cheesecake
Tap water
Probably any ethnic food, outside (or sometimes including) its home country.
I will say tortilla espanola (pretend that n has a tilde), and particularly the sandwich made from it. This is a potato omelet typical of Spain. I think it has to do with the high quality olive oil and the eggs that are not factory farmed. I have made them myself here, but it is not the same. Also, Spanish bread is not exactly like French bread. Finally, I think it is a food that depends a fair amount on technique to get the proportions, temperature and timing exactly right. Because clearly, it is not down to any fancy secret ingredients. I try, I try, it is not the same. 
I will also give a shout-out to Spanish paella. I’ve never had it quite right here in the US, and God knows saffron risotto is not the same thing!
There is a restaurant that purports to be authentic Mexican in Little Rock. It was horrible when I tried it several years ago. 
I refuse to believe you can get better Mexican or Tex-mex in New York than you can in select small Texas towns.
Authentic Chinese is tricky, but I know one restaurant near me (relatively near, at least, but very close to my work) that serves the good stuff on the weekends. Come for the General Tso’s and you’ll be disappointed. Stay for scallion pancakes and you’ll promise to be a good person for the rest of your life if you can keep eating.
There are probably a number of different answers - including, in some cases, that the food might well be authentic! The one that comes to mind is that the restaurants are businesses first and exporters of their native culture only a distant second. If your customers are going to love authentic food, that’ll be great. But in many cases, what customers really seem to want is something that gives the impression of authenticity while actually catering to their own tastes!
The most obvious example of this for a Briton is the ubiquitous ‘Indian’ food. (The majority of such restaurants I’ve run into are actually run by emigrants from Bangladesh or Pakistan.) It’s really, really good - and not particularly closely related to the food actually eaten in vast swathes of India. The adaptation to local taste is possibly best illustrated by the fact that despite many (most?) Indians being vegetarian, Indian restaurants in the UK tend to serve meat almost exclusively. (Some of this is explained as Pakistan and Bangladesh are much less vegetarian than India.) Additionally, I’ve never had someone from India cook me anything nearly as heavy on the chilli powder as the vindaloos and - god forbid - the phaals in Indian restaurants. As a further illustration of the adaptation, the most popular dish in the UK is said to be chicken tikka masala, which may well have been invented at an Indian restaurant in the UK!
Try telling that to someone who lives near San Francisco.
the best…
sausage dog – toronto. (yo, 1 spicy sausage, dog!) there are a usually a dozen toppings offered, but only three really should ever be used; onion, sauerkraut, & mustard. that’s how you do a sausage, dog.
gyros – london, ontario. sammy souvlaki stands have the best gyros (it’s pronounced “yee-ros”) ever. gyros with everything; that’s lamb, onion, tomato, tatziki, & tahina wrapped in a pita.
poutine – quebec (i say quebec city, but i don’t really know the rest of the province very well.) chez ashton has better poutine than anywhere outside of pq, and i have stumbled into a few places in qc that put chez ashton to shame.
pretzels – gotta say nyc here. never have i had a better pretzel than hot off a cart, slightly drizzled with mustard, than my time in new york.
moose – northern ontario. some poeple can’t handle the moose, but it is my all-time favourite meat. hard to come by in the city, but every time i’m up north, i gots to gets me some moose steaks. damn thats some good eatin.
Pizza.
New York.
Period.
I agree with you, but technically it’s East Carolina. The vinegar based Bar-B-Que is the best. That tomato flavored corn syrup stuff people pass off as barbeque sauce is unacceptable.
I don’t care what anyone from Louisiana says: Blue crabs without Old Bay are unholy, and they should only ever be steamed.
The smoked salmon prepared on the reserves of the First Nations peoples in British Columbia is pretty freaking amazing.