Begin with the stock. Smash the ginger and knot the scallions. If using the dried flatfish, toast it in a dry oven until golden before adding it to the pot. Blanch the hen, pork bones, and pork skin in boiling water for 8 to 10 minutes, then drain and rinse off the scum. Combine everything — the blanched meats and bones, the ham, dried scallop, dried shrimp, toasted flatfish, water, ginger, scallions, and Shaoxing wine — in a large stockpot and bring to a boil. Skim quickly, before the fat renders and binds to the scum, since once the oil emulsifies it becomes far harder to clear. Drop to a bare simmer and cook for 4 to 6 hours, until the stock reduces to about 5⅓ quarts of glossy, savory liquid, then strain and reserve it.

While the stock simmers, build the spice bag. Smash the galangal. Crack open the green cardamom, tsaoko pods, monk fruit, and white peppercorns — crack large pods, but do not grind anything to powder — and bruise the lemongrass stalk. Dry-toast the hard, resinous spices — star anise, cassia, green cardamom, fennel seed, tsaoko, Sichuan peppercorns, white peppercorns, dried chili, and the bay leaves, the last only lightly — in a dry pan until fragrant, since this volatilizes their aromatics. Do not toast the clean-scented spices — sand ginger, aged tangerine peel, licorice root, clove, monk fruit, or gardenia fruit — because heat drives off their delicate top notes and can coax out bitterness; galangal, amomum, and angelica root need no toasting at all. If you like, bloom the toasted spices briefly in a splash of high-proof baijiu, then bundle everything into a muslin bag or spice pouch.

Next, prepare the seasoning. Reserve 3 ounces of the rock sugar for the caramel and set the rest aside to go directly into the brine. To make the caramel, melt the reserved rock sugar in a dry pan over low heat, undisturbed, until it turns deep amber and bubbles, then pull it from the heat and carefully deglaze with a ladle of the hot stock — it will spit — stirring until smooth. This caramel is the brine’s primary source of color; the dark soy sauce plays only a supporting role. Salt the brine to about 2.5 percent of its total liquid weight as a starting point, and plan to adjust once you taste the finished sauce.

For the aromatic oil, heat the fat in a pan and fry the scallions, ginger, garlic, shallots, cilantro roots, and celery gently until golden and fragrant, about 5 minutes. If using, add the pandan leaf, bruised or torn, in the last minute only, since it is optional but recommended in the deep-southern style and needs no more than a brief infusion — one leaf is enough, and its presence should be felt rather than named. Strain the mixture: the oil goes into the brine, where it becomes the fragrant fat cap, and the fried solids go into a second muslin bag to steep briefly in the finished brine.

To assemble, bring the strained stock to a simmer and stir in all of the seasoning — the soy sauces, oyster sauce, fish sauce, rock sugar, maltose, wines, caramel, and salt. Add the spice bag and simmer gently, uncovered, for 45 to 60 minutes, no longer, or the brine turns medicinal and bitter. In the last 15 minutes, pour in the aromatic oil and drop in the fried-vegetable bag. Taste and balance the brine, which should read salty-savory first, gently sweet beneath, deeply aromatic, and warm amber-red in color; correct the salt toward 2.5 percent, the sugar for roundness, and the dark soy for color, adjusting a little at a time. Remove the spice bag once the hour is up, since leaving it in indefinitely over-extracts the brine and muddies its flavor — a fresh bag is used on each future refresh. Once assembled, the master sauce is ready to braise a first batch of soy-sauce chicken, pork belly, eggs, or the braised soybeans immediately, or it can be cooled and stored to mature.

A master sauce is a living thing, tended like a sourdough mother, and every source agrees that it only deepens with age — a decades-old brine is a genuine treasure. After every use, skim the surface and strain out all debris and dregs, since the settled sediment at the bottom will sour the brine if left in, then return the pot to a hard boil for a few minutes to sterilize it. A resting brine naturally settles into four layers — an oil cap on top, a layer of foam, the brine itself, and dregs at the bottom — and the oil cap should be kept, since it seals and perfumes the sauce, while the foam and dregs should be cleared away.

To store the brine in the refrigerator, boil it first and let it cool uncovered until the fat cap sets, since covering it while it is still steaming lets condensation drip back past the seal and spoils the sauce; for infrequent use the brine can be frozen, and it barely solidifies thanks to its salt and sugar content. Each time the brine is used again, replenish it in the spirit of a mother dough: top up the stock, add roughly a quarter of the original quantity of soy sauce, include a fresh spice bag, and add a little more rock sugar and salt, rebalancing the color and salinity as you go — never simply add soy sauce on its own, or the brine will drift dark and flat over time. The aged flavor-oil that collects atop a long-kept brine is especially prized for its power to lift and deepen other dishes, so it is worth guarding carefully.