Can you elaborate on which empanadas you are referring to?

Spain has several versions, but the most famous of these are the empanadas gallegas and as the Galicians are amongst the most travelled of all the Spaniards I wouldn't be surprised if their versions have influenced the empanadas in Argentina and other parts of South America.

Whoever made this webpage is obviously a bit of an empanada connoisseur
http://www.spanishnewyork.com/spanis...-new-york.html
and amongst the recommendations are lots of mentions of empanadas with comments on those that are good and those that are best avoided.
Out of the suggestions I'd be swayed by:
Costa del Sol
369 West 50th Street, New York
(212) 541-8382
Which specifically mentions Empanada Gallega (which should be ordered in advance) and that the owner is from Galicia. Both of these are a good sign.

I'm very partial to the empanadas from Alicante (particularly those with 'pisto' and with pisto and tuna). For my wedding reception I asked an aunt to bring a selection from Spain with her... delicious! And didn't last long at all. I've no idea where you'd get anything as nice as those in London.