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Hey YOU. Back of the line...
The venue: Ada Scallion Pancake.

The item: Scallion pancake (cong you bing, 葱油饼), a Shanghainese traditional street food that is pork fat and scallions inside folded dough. Normally costs around 3.5rmb.
The wait: You'll need to queue up before 6am to get a number (which is written directly on your hand -- no funny business). That's limited to 50 people only. The waiting time is around 2 to 3 hours if you don't have one. We waited for a brisk 45 minutes; you'll find out why later.