To make the dashi broth, carefully wipe the kombu with a cloth but do not wash. Slowly boil the kombu in 800 ml water on a medium heat. As soon as the water begins to bubble remove the kombu. Then allow the water to boil.
Add the bonito flakes to the pot and bring to the boil again. Wait approx. 1 minute until the flakes sink to the bottom and then strain the broth through a cloth.
Heat the broth once again and stir in the miso paste until it is completely dissolved. Season with salt and ground black pepper. Add the tofu and simmer for 4-5 minutes. Season again.
Serve the soup in bowls and add the bean sprouts and the herbs. If desired serve with a dollop of chilli sauce.