Basi (Sweet Potato in a Molten Sugar Shell)

Variations

• Basi shanyao (拔丝山药): the same treatment for Chinese yam. It holds more water and is slippery cut, so dry it more carefully before it goes in the oil. It is less sweet in itself, which lets the sugar shell stand out.
• Basi pingguo (拔丝苹果): with apple, the pieces are battered in a starch slurry and fried first. Apple gives up water as it heats, so it needs a layer between it and the sugar.
• Whether to scatter sesame: it adds aroma and keeps the pieces from welding to each other quite so fast. It also hides the shell, which is why plenty of cooks leave it off.
• Set beside tanghulu: tanghulu dissolves its sugar in water and boils it to 150-155C. This one uses no water at all. Both end in a shell that breaks like glass, but they get there by different routes, which the tips below are about.

Tips

• Every rung on what sugar does' ladder is a water syrup, and there is no water in this dish. That guide traces the jobs sugar takes on when it is the main ingredient back to one fact — "sugar binds water so that nothing else can use it." — and each step on its temperature ladder is really a reading of how much water is left. It parks tanghulu at 155C, where the syrup "drives nearly all the water out so it shatters like glass.", which is the ladder at its clearest. Basi never dissolves its sugar. With no water to drive off there is no rung to stop at: the sugar melts and goes straight on towards colour, and what sets the pan's temperature is the oil underneath rather than the sugar itself.
• So the same thread means opposite things in the two dishes. Tanghulu writes "A drop of syrup that pulls into threads is not there yet (soft ball to soft crack)" — there, a thread means not yet. Here it means done. Not a contradiction: the two are measuring different things. Tanghulu drops syrup into cold water and reads a temperature from it; basi reads the viscosity of the melted sugar itself, in air. Sugar with no water in it draws out a long thread that does not snap, and that property is what the dish is named after.
• Waiting for colour is waiting too long. The guide is blunt about it: "By the time you see the colour you want, you are late." A thin film of sugar over oil moves faster still. Lift the spatula at pale amber, look for the thread, and kill the heat there.
• Hong shao rou is one step back from this. That page separates melting sugar dry from stirring it into liquid — "melting it dry first is not interchangeable with stirring sugar into the braising liquid." — and basi goes a step further again: not a dry pan but a filmed one. The oil keeps the sugar off the metal, and it also makes the finished shell let go of the plate and the chopsticks more willingly.
• No glucose syrup, no honey. Adding syrup to stop the sugar recrystallising is a trick that belongs to sugar dissolved in water. Here the water it brings is the problem, and the shell stays tacky instead of shattering — the exact opposite of tanghulu, which stirs in a tablespoon of it on purpose.
• The bowl of cold water is equipment, not a garnish. Talk about the sugar ladder usually ends with choosing, in the pan, the texture you want later. This dish declines to choose: the setting happens at the table, in the hand of the person eating, so there is nothing to decide on the stove. A dipped piece is hard on the outside and still hot inside.
• Oil the plate. Set sugar does not come off a bare dish. A film of oil between the two lets the pieces lift cleanly. For the pan, add water and bring it to the boil — dissolve it rather than scraping it.
• It only works hot. Cooled, the threads stop and the shells weld the pieces into one lump. In the terms serving temperature uses, this is food that cannot wait: you do not make it and then call people, you carry it to a table where they are already sitting.