This recipe is one of the most basic soup recipes in Japan and was very popular on the menu in Otabe Kafe in Putney. Please also have look at the interview article about this dish.
This basic recipe is really good because once you get familiar with it, you can make different dishes by just changing the toppings. For example, when you are busy, you can just put chopped vegetables in it. When you are really hungry and want to eat it as a main dish, you could put some Tempura on top. It looks gorgeous and Tempura soaked in Dashi soup is just amazing!