Cong You Bing (Layered Scallion Flatbread)

Variations

• Folded instead of rolled: the method ko.wikipedia describes stacks the sheet in folds rather than winding it. Folded like a fan and then pressed out, the layers run in parallel; wound into a coil they run in rings and the centre is thicker. Both are sold from the same stall.
• The thick Taiwanese kind: rolled to 1.5cm, so the outside crisps and the inside stays chewy. This is the one night markets crack an egg onto.
• Zhua bing: after frying, it is crushed in from all sides with tongs until the layers come completely apart. Same dough, different finish, and the commonest form in Taiwan.
• Other fillings: garlic chives, chives, or rendered lard in place of the oil. Lard splits the layers more decisively and sets hard as it cools.
• To dip: soy with black vinegar and chilli oil, or garlic soy. With soy milk beside it, that is breakfast in northern China.
• Against roti canai: both coil a stretched sheet to build layers, and they put opposite things between the turns. The first Tip is that story.
• Against haemul-pajeon: the comparison ko.wikipedia reaches for first when it explains this bread. The same scallion, laid under a thin batter there and shut inside a stiff dough here. The Tips come back to it.

Tips

• It is rolled with a pin and keeps its layers, because what is between them is a solid. Roti canai makes the same coil and states the opposite: "A pin presses the layers into each other and you end up with a flatbread" What holds that bread's layers apart is liquid oil, so a pin drives it sideways and the dough meets dough and welds. Cong you bing has a stiff flour-and-oil paste and chopped scallion between its turns. Pressed, they stay where they are and keep the surfaces from touching. The same action is a failure in one bread and a step in the other.
• The flour that page forbids is an ingredient here. Roti canai will not have flour on the worktop, and gives the reason: "Flour dries the sheet and welds the layers" That is right, and it is about flour arriving dry between the layers instead of oil. The flour in you su is not dry powder, it is a paste beaten into oil. The same substance is glue in one state and a barrier in the other.
• The scallion's water lifts the layers from inside. Roti canai says why its layers separate: "Fold the stretched sheet and griddle it and you have a thin bread. Folding it into a strip and rolling that into a spiral is what traps oil between the turns so it separates in the pan" There the oil does it. Here the finely cut scallion gives up water in the pan, and that water becomes steam inside 6-7mm of dough and prises the layers apart. Which is why too little scallion means fewer layers — it is a raising agent as much as a flavour (steaming covers what trapped steam does).
• Which is also why the pan stays uncovered. That steam has to do its work between the layers and then leave. Under a lid it cannot go up, so it falls back onto the surface and the face that should be crisp goes soggy.
• Half the water goes in boiling. Hot water gelatinises part of the starch and slackens the gluten network, which is what lets the sheet go to 2mm without tearing (dough and gluten). All boiling water and it is too soft to hold layers; all cold and it springs back and will not roll thin.
• Of the two rests, the second matters more. Roll the coil straight away and the dough springs back and pushes the paste out through the seam. Fifteen minutes is enough, and in that time the scallion wets the surface and makes the rolling easier too.
• The scallion is handled in the opposite direction from haemul-pajeon. That page sets out its own architecture: "the batter is poured over them; the seafood is scattered on top and a little more batter drizzled after" There the scallion is laid down and the batter is the minimum needed to hold it. Here the scallion is shut inside and the dough is the subject. Which is why that one may be turned only once and this one can take a rolling pin.
• Medium-low, and long. Over high heat the outside sets before the inner layers have anywhere to expand into. Four or five minutes looks long, and it is the time the layers are being made (heat control).
• Crush it when it comes out. The same move roti canai calls kepuk. It pulls apart the layers that did stick, and doing it or not is the clearest difference in the eating.
• Freeze it before it is rolled. Freeze the coiled snails, thaw in the fridge, then press and fry. Frozen after frying, the layers go limp on reheating (reviving leftovers).