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1
Place the pork bones in cold water, bring to a boil, and drain immediately. Rinse the bones under cold running water to remove blood and impurities. Return the bones to a clean pot with 2 litres of cold water. Bring to a gentle simmer. Add the niboshi (heads and guts removed). Maintain a low simmer for 3–4 hours without vigorous boiling — some opacity from dissolved pork collagen is correct and expected. The broth is ready when it carries a clear, savoury depth with a distinct sardine-umami undertone.
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2
Strain the broth through a fine sieve. Do not press solids. Set aside. The finished liquid should be clear but not crystal-bright — a faint collagen haze is characteristic of Kitakata style.
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3
Combine shoyu and mirin for the tare. Warm briefly over low heat until the raw alcohol of the mirin dissipates — detectable by smell. Remove from heat and reserve. This tare is not added to the broth pot; it is portioned per bowl at service.
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4
Tie the pork belly into a tight log with kitchen string. Heat neutral oil in a heavy pan over high heat and sear the log on all sides until a deep mahogany crust forms — this is confirmed by even colour across every surface. Transfer the seared log to a snug pot. Add the shoyu-mirin braising tare. Add enough water to nearly submerge. Braise at the lowest possible simmer, covered, for 2–3 hours. This is where the dish lives or dies: insufficient time leaves the collagen unconverted and the fat unrendered; the chashu must yield without resistance when pressed, and the braising liquid must have thickened perceptibly around the pork.
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5
Remove the chashu from its braising liquid. Allow to cool sufficiently to slice cleanly. Cut into thick rounds — generous portions are the regional standard. Reserve the braising liquid; it may be incorporated into the tare at service.
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6
Bring a large pot of unsalted water to a rolling boil. Cook the hoshi chūkamen according to the noodle producer's specification for this hydration level (40–45%). High-hydration noodles cook quickly; the finished noodle must be soft and yielding, not firm. Drain immediately.
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7
For each bowl: add the shoyu tare to a warmed bowl first. Ladle the hot broth over the tare and stir briefly to combine. Add the drained noodles. Lay thick slices of chashu across the noodles. Spoon 20 g of lard over the surface. Do not stir the lard in and do not skim it — the visible fat layer is a functional flavour component, not a defect. Serve immediately; the lard will melt into the broth as the diner eats.