Cao lau, the noodle that refuses to leave Hoi An

Every Vietnamese dish that travels has a version in Hanoi and a version in Saigon. Cao lau has neither. It is sold in one town of about 150,000 people and, for practical purposes, nowhere else.

What is in a bowl of cao lau?

A bowl of cao lau holds thick pale-brown noodles, slices of marinated pork, a handful of fresh greens, crisp fried squares and a few spoonfuls of dark sauce. There is no broth to speak of.

The noodles are the reason the dish exists. They are dense and chewy, thicker than any other Vietnamese rice noodle, and closer in bite to udon than to the flat sheets used for pho.

The pork is marinated with soy and five spice, roasted, and sliced thin. It is the Chinese half of the bowl, and it tastes like it.

Why does it not leave the town?

Hoi An cooks give a specific answer: the noodles need water from the town's old wells and lye made from ash carried off Cham Island, and neither substitutes. The Ba Le well is the one usually named.

Treat that as the local account rather than settled chemistry. What is verifiable is the practical half — a small number of families make the noodles, they sell them fresh within the town, and nobody ships them.

The result is the same either way. Cao lau on a menu outside Hoi An is made with substitute noodles, and the substitute is the part of the dish that mattered.

Is it Japanese or Chinese?

Cao lau's ancestry is claimed by two trading traditions, and neither claim is settled. Hoi An was an international port from roughly the 15th to the 19th century, trading with Japan, China, Portugal and the Netherlands, and it kept a Japanese quarter during part of that period.

The Japanese theory points at the noodles, which behave like soba in their density and their treatment with lye. The Chinese theory points at everything else: the five-spice pork, the dark sauce, the name itself.

A trading port that ran for four centuries is allowed to produce a dish with two parents. The architecture guide covers what the same period left standing above ground.

What are the crisp squares for?

The squares are cut from the noodle dough, deep fried until they puff, and served on top. They are structural rather than decorative, because a bowl this dry needs the contrast.

Break them into the bowl rather than eating them separately. They soften slowly, which means the last mouthfuls have a different texture from the first.

Some kitchens add pork crackling as well. That is a house choice rather than a rule, and it is not a sign of a better bowl.

Where should you eat it?

Hoi An central market and the neighbourhood kitchens away from the river, rather than the restaurants with English boards and a view. The market food court sells the dish at the price the town pays.

The greens come from Tra Que, the herb village about 3 km from the old town, which supplies most of the restaurants here. A bowl with a full plate of those greens is the bowl to want.

Hoi An's old town charges 120,000 dong for its heritage ticket and nothing for its food streets, and the food streets are where this dish lives. The three days in Hoi An route puts the market visit on the first morning.

What does a bowl cost?

Thirty to fifty thousand dong at a market stall, which is one to two dollars at about 26,000 dong to the US dollar. The riverfront restaurants charge 80,000 to 150,000 for the same bowl.

The gap between the stall and the riverfront is the widest of any dish in the town, because cao lau is what a visitor asks for by name. A kitchen with a queue of Vietnamese diners is charging the lower number.

The cheap eating guide covers how to read the difference before sitting down rather than after.

How is it different from mi quang?

Cao lau and mi quang come from the same stretch of coast and share almost nothing. Mi Quang uses wide turmeric noodles, crushed peanuts and a sesame cracker, and belongs to the whole province. Cao lau uses thick brown noodles, crisp squares and roast pork, and belongs to one town.

Cao lau and mi quang are both low-broth bowls that get mixed rather than spooned, which is the regional habit they do share. The noodle soup guide covers where each sits among the country's wetter bowls.

Eat them a day apart rather than in one sitting. They are similar enough on paper that the differences only land when the bowls are separate.

When do kitchens sell it?

Cao lau is sold from morning until the noodles run out, and the market kitchens start before eight. A stall that made its noodles at dawn has them for the day and then stops.

Evening service exists in the old town, aimed at visitors, and it is the weaker option. The greens have wilted through a hot afternoon and the crisp squares have given up.

Eat it at lunch, before the town fills. Hoi An turns over at about five in the afternoon, when the lanterns come on and the streets stop being walkable at any speed.

Can you eat it without the pork?

A vegetarian bowl exists in Hoi An, and the town makes it more seriously than most places would. The kitchens around the pagodas cook chay food on the first and fifteenth days of the lunar month, and several sell a cao lau chay year round.

The pork comes out and fried tofu or seitan goes in, with the same noodles, greens and crisp squares. The sauce is rebuilt on soy and mushroom rather than meat.

Say chay when you order and the kitchen will tell you whether it has one. The vegetarian guide covers how that word works across the country.