So I kept looking for articles on "su bing" (how Shanghai bun in Matawan ,NJ spells it), especially on wikipedia, my preferred encyclopedia. Eventually I found it's usually written "Shaobing", and found out more about it.
To describe what it is (don't get me wrong, I've been eating them at Shanghai Bun, so I know what they're like, I just wanted to know more details about it), it's a kind of filled pastry, with a flaky crust. Can be filled with a peanut mixture, or radish, or other things. At Shanghai Bun the peanut mix is delicious, a wonderful peanutty thing that's somewhere between sweet and savoury. The radish su bing there has a nice soft texture inside.
Anyway, what I found interesting looking up online is how they make the pastry flaky. Flakiness in pastry is made by layers of fat smushed into the dough, the fat prevents the dough from sticking to itself in those spots, and so you get sort of layered pastry, and the fat crisps those places too, so in aggregate you get flakiness.
Normally this is done by cutting in a solid fat into a flour mixture, then rolling the duogh, keeping everything cold.
However, all the recipes for shaobing describe a process that makes sense that it would work, but it's different. basically, you make a roux, and then spread that on a sheet of dough you roll out. Then you fold and roll out again the sheet of dough, to make the layers. Similar to how croissants are made, but with a liquid, vegetable oil roux.
So reading about this, it makes sense that it would work. You've got the fat, you've got the layers, it's just the use of roux is interesting. I'm thinking one advantage of roux is that it's sort of "sticky", because it's got flour in it, it helps stick the dough together better.
Just one of those funny things.
Thoughts...? Anyone heard of this before?