Heat a frying pan over medium heat and coat with the sesame oil. Roast the sardine for 1 to 2 minutes each side. Add miso paste and roast until the miso becomes fragrant.
Pour the sake and add the ginger. Evaporate alcohol.
Add the water and bring to a boil. Just before turning off the heat, mix in the soup base.
In a large pot, bring water to a boil and cook the noodles for 1 minute and 30 seconds. Drain well and add the sesame oil to prevent the noodles from clumping. Transfer to another serving bowl. (If you prefer the noodles to be cold, wash the noodles in ice-cold water and drain well.) Place the egg and braised bamboo shoots and sprinkle the nori seaweed.
Warm up the dipping sauce from Step 4 and pour into a serving bowl and place the narutomaki, spring onion, and onion. Add the vinegar if using. Enjoy!