Generally in eastern Japan, in areas such as Kanto, it is a clear soup flavoured with dashi and soy sauce. The mochi it is served with is cut into a rectangle and lightly browned on a grill.
In western Japan (in areas such as Kyoto, Kansai and Osaka), Zoni is an opaque soup, with white miso paste added. But the further west you go, the clearer the soup gets again. It is served with round mochi. In some areas, though, largely islands or on mountains where rice is not prevalent, mochi is replaced with taro or tofu. The mochi is heated by simmering, then put in the soup bowl first by itself. Then the soup is added and adorned with some food garnishes cut into round pieces.
Some form of protein is added (chicken, fish or salted fish, or meatballs.) Garnishes can include Japanese Mustard Spinach (aka “komatsuna” in Japanese), Trefoil (aka “mitsuba” in Japanese), sliced steamed fish loaf (aka “Kamaboko” in Japanese), and yuzu zest. Shichimi Togarashi provided at the table for an additional garnish to taste.
Using different coloured slices of steamed fish loaf adds to the festive look. Some people to leave a few roots on the Japanese Mustard Spinach to signify a wish to descendants. Some prefer to make most ingredients separately, them combine and heat through, to keep all the flavours separate.
Some regions put Sweet Red Bean Paste inside the balls of mochi (aka “Azuki an” in Japanese.)
Despite the variations that occur from region to region, each region does not vary from what is typical for it. If you tell someone what the Zoni you were served as a child had in it, they call reputedly tell where you grew up. If a couple is from different parts of Japan, on New Year’s Day they may make one version and then on 2 January the other version. That being said, some families have their own “traditional” version of Zoni that has nothing to do with the region they live in, and regional distinctions are gradually fading.
In the part of northern Honshu, Zoni is called “Tohoku.”
It is also common in some areas to first make a soup called “noppei-jiru”, and then use that as the base for Zoni.
Zoni can be made ahead and then stored in the refrigerator and assembled and heated at the last minute.
It is served for breakfast on New Year’s morning.
Koreans make a similar soup called “tok-kook.” Mochi in Korean are called “kare-tok.”
Mochi cakes are sticky to begin with, and get even stickier in the soup, making them somewhat tricky to eat. Every New Year, there’s always a few people, usually older folk, who choke to death while eating the rice cake soup.
The serving of Zoni at New Year reputedly dates from the 1500s. It is supposed to bring good luck.
“Zo” means “this and that” or “mixed”; “ni” means “boiled.”
Sometimes in English Zoni is called “Mochi Soup”. Zoni means “mixed food”.
Sometimes called “Ozoni.”