Clams and spring onion are simmered in miso and poured straight over rice. That is the entire dish, and there is no step you could remove from it. It is quick and nourishing. It can be made on a boat, which turns out to explain everything about it.

In the Edo period the district now called Koto was a shallow bay, Fukagawa-ura, where the tide went out far enough to expose sandbanks. The fishermen there held a licence from the shogunate to work those flats, and clams could be had almost for the taking. What they cooked between jobs, for themselves, is what the city later put on menus under the name of the place.

There is a second version, cooked into the rice with soy sauce rather than ladled over it. That one is said to have been developed so it could be carried, in a box, by carpenters and other tradesmen. Same shellfish, two settlements: the soupy one belongs to the water, the packed one to the land.

The sea is a long way from Fukagawa now, held back by concrete and filled in for decades. The name has comfortably outlasted the ground it once referred to, which is a fairly ordinary fate for a Tokyo neighbourhood and still worth noticing over a bowl.