Cold-soak, blanch, and scrub every bone

Refrigerate the pork bones under cold water for 6–12 hours, changing the water twice; never soak on the counter. Cover with fresh water, boil hard for 15–20 minutes until the heavy grey foam subsides, drain, and discard that water. Under running water, scrub each bone and pick dark clots from every crevice. Wash the stockpot before the real broth begins. At the same time, refrigerate the tare soy, mirin, sake, kombu, and cleaned niboshi to cold-steep overnight.