Remove the heads and innards from the dried sardines.

Combine the sardines and kombu with the water and let soak for about 1 hour.

Heat over medium heat and remove the kombu just before it comes to a boil.

Once boiling, add the bonito flakes, skim off any foam, then simmer over low heat for 10 to 15 minutes.

Strain the dashi and set aside.

Gently heat the white dashi.

Bring to a boil, add the mirin and sugar, and stir until dissolved.

Stir in the soy sauce and bonito flakes, remove from the heat, and let cool completely.

Strain the sauce and set aside.

Dissolve the salt in the water.

Pour the salted water all at once over the flour in a large mixing bowl. Mix with your fingertips for 1 minute, then continue for 8 to 9 minutes until crumbly, rounded pieces form.

Gather the dough into a sturdy bag and flatten it. Step on the bag to knead, then fold and repeat several times until smooth — about 3 rounds of 1 minute each — first shaping into a rectangle, then a square. Shape into a ball and seal tightly.

Let rest for 5 to 10 minutes, then flatten once more.

On a well-floured surface, roll out the dough gradually, turning as you go, until about 3 mm thick. Flour generously, fold accordion-style, and cut into 3 mm-wide strips. Unfold the noodles and shake off any excess flour.

Bring a large pot of water to a rolling boil. Add the noodles, gently untangle them, and cook for about 13 minutes.

Rinse the noodles under cold running water to remove excess starch, chill thoroughly, and drain well.

Divide the noodles among bowls, add the toppings, and spoon a little bukkake sauce over the top — just enough to coat, not to serve as a soup.