Unagi kabayaki

Kanto, the Tokyo method. Split along the back and the head removed. The fillets are skewered and grilled plain, then steamed, then grilled again while being repeatedly dipped in tare, a sweet soy glaze. The steaming step is the distinguishing one: it renders out a large part of the fat and collapses the connective tissue, producing eel so soft it can be eaten without much chewing.

Kansai, the Osaka method. Split along the belly, the head often kept on during cooking to hold the fillet straight and removed at the end. Grilled from raw straight through over charcoal with no steaming, so the skin crisps and the flesh stays firm, oilier and more directly smoky.

Neither is better and people have preferences the way they have preferences about barbecue. If you have only eaten unagi in Tokyo you have eaten the soft version, and the Osaka one will surprise you.

The tare itself is worth knowing about. Long-established restaurants keep a master sauce, topped up rather than replaced, which in some houses is claimed to descend from a batch started generations ago. Whatever the provenance, the sauce is the restaurant’s signature and is not bought in.

Unaju is eel over rice in a lacquered box, and it is the standard order. Unadon is the same thing in a bowl, usually cheaper and slightly less ceremonial. Grades – often matsu, take, ume, pine, bamboo and plum – indicate the quantity of eel rather than the quality, so the cheapest grade is the same fish in a smaller portion.

Kimosui, a clear soup with the eel liver in it, is the traditional accompaniment and is usually ordered separately. Sansho pepper comes on the table: it is not chilli heat but a citrus-numbing spice that cuts the fat, and a proper pinch improves the dish considerably.

In Nagoya there is a third format, hitsumabushi, in which you eat the box in quarters – plain, with condiments, with dashi poured over as tea-rice, and then whichever way you liked best. Some Tokyo restaurants offer it.

Expect to pay. Unagi is one of the most expensive everyday dishes in Japan and prices have risen with declining eel stocks. A good unaju in Tokyo is a several-thousand-yen lunch, and a specialist house is more.

The traditional day is Doyo no Ushi no Hi, the midsummer Day of the Ox, when eel is eaten for stamina in the heat. Restaurants queue out of the door and prices go up. It is a genuine custom and a poor day to try it for the first time.

Asakusa and the old low city are the traditional Tokyo districts for it and the Asakusa page covers the neighbourhood. Many specialist houses are small, open for a lunch and a dinner service, and take bookings; eel is cooked to order and takes thirty to forty minutes, so this is not a quick meal.

The awkward part is conservation. The Japanese eel is listed as endangered and stocks have fallen sharply; almost all farmed eel is raised from wild-caught juveniles rather than bred in captivity, so farming does not currently relieve the pressure. That is a reason to eat it thoughtfully at a good restaurant rather than casually from a supermarket, and it is a reason some people decline it altogether. Both positions are defensible and we are not going to pretend the question does not exist.