Put the ingredients marked with in a small saucepan, then add the water little by little while mixing to dissolve the miso paste. Place the pan on the stove and heat. Boil the noodles.
Once the soup is bubbling, add the dissolved katakuriko to thicken the soup, then pour the beaten egg in. Add the vinegar and mix the soup quickly before adding the salt, pepper and sesame oil at the end.
Add the noodles and as much ra-yu chili sesame oil as you like.
I made this with white miso. It was super delicious too.