Small potatoes are simmered whole in their skins with miso until the liquid has reduced and they take on a shine. Thin-skinned new potatoes are used, so the dish runs from about March to July, and the skins are eaten along with everything else rather than peeled away.

The seida in the name is a man. In the late Edo period a magistrate posted to Kofu, Nakai Seidayu, sent to Kyushu for potatoes and distributed seed tubers to the villages of the province. The crop is credited with carrying people through a famine. Afterwards they began calling the potato by his name, and over time the name wore down to seida. Tamaji simply means the small ones.

He was subsequently enshrined as a god of the potato, which is a considerable career outcome for a provincial administrator. A stone marker to him still stands at a temple in Uenohara, and the potato kept his name long after the office he held was abolished.

It happens now and then that a food is named after a person. What is unusual here is the direction of it. The people who were fed did the naming, and then kept on saying it for two hundred years, by which time the name had worn down to two syllables and most of them had forgotten it was a name at all.