Bring about a liter of water (not listed) to a boil, and add the chirimen jako. When the water comes back to a boil, drain the chirimen jako through a sieve.
Add the parboiled chirimen jako, kombu based dashi stock, sake, sugar and vinegar to the pan and heat. Turn the heat down to low when it comes to a boil, and simmer for about 3 minutes.
Add the soy sauce and mirin and continue simmering over low heat. When the liquid in the pan has reduced by half, add the sansho peppercorns, and mix with chopsticks while simmering and reducing the sauce.
When there's almost no moisture left in the pan, remove it from the heat. Spread it out on a flat plate to cool. Pack into sealed containers when cooled and store in the refrigerator.
Story Behind this Recipe
I wanted to eat a mildly spicy version of chirimen sansho, so I came up with this recipe. By using kombu based dashi stock and vinegar, I think the flavor become mild and quite complex.
I used sansho peppercorn tsukudani (cooked/preserved in a salty-sweet soy sauce based sauce). If you are using fresh sansho peppercorns, parboil before use.