I'm talking authentic, complex, fresh biryani. Where can I find it? This applies to any of the five boroughs.
I'd have to say the Biryani Cart in the Theater District - Times Square. It's become a bit of a legend in the past few years and as long as you're OK with food from a cart this is a GREAT place for Biryani. I opt for their shrimp but I'm sure it's all pretty good. Just make sure you have time to stand in line as this is a very popular place.
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For an "upmarket" briyani, I recommend Tamarind Tribeca. It is a beautiful restaurant, a bit pricey and refined (like eating at the Oberoi in Bombay), in a modern but still "white table cloth" kind of way. The food is fantastic. I am getting hungry just thinking about it.
I haven't had that many biryanis but I can direct you to a neighborhood with the most authentic Indian food. That's Jackson Heights, NY. This neighborhood is probably the most diverse in terms of food, and has some of the best Indian, Pakistani, Nepalese restaurants in all of New York City.
Like I said, I have not sampled many biryani's in the city, but I'm sure here is where you'll find them.