udon is most often served hot as a noodle soup in a mild, salty broth. its simplest form is called "kake udon". this consists only of dashi stock, soy sauce ("shōyu"), mirin, and "udon" noodles. different things can be put on top of the soup as toppings. often thinly cut scallions are used, along with other common toppings such as kamaboko, prawn or vegetable tempura, some spices, and wakame.