Though ingredients will vary by region and by family tradition, typically they will include shrimp, gelatin, daikon radish, carrot, mochi, dashi and soy sauce. You make a thin, light soup out of these ingredients. In eastern Japan the soup is left clear; in western Japan white miso is added to make it opaque.
The rice cakes, “mochi”, are heated in a frying pan, then put into a bowl, poured over with the soup, and served garnished with yuzu zest.
Mochi cakes are sticky enough 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.
Koreans make a similar soup called “tok-kook.” Mochi in Korean are called “kare-tok.”
Sometimes in English Ozoni is called “Mochi Soup”. Ozoni means “mixed food”.