Udon is a type of thick wheat flour noodle popular in Japanese cuisine. Udon is usually served hot as noodle soup in broth in its simplest form. It is usually topped with thinly chopped scallions. Other common toppings include tempura. A thin slice of kamaboko, a halfmoon-shaped fish cake, is often added. The flavor of broth and topping vary from region to region. Usually, dark brown broth, made from dark soy sauce, is used in eastern Japan, and light brown broth, made from light soy sauce is used in western Japan.