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1
Place the trotters in a large pot of cold water. Bring to the boil and blanch for 5 minutes, skimming the grey foam that rises. Drain, rinse under cold running water, and pat dry. The water should run clear before the trotters leave the pot.
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2
Heat the oil in a wide heavy pot over medium heat. Add the trotters in a single layer and brown on all sides, turning with tongs, until the skin shows a uniform amber-gold. This step develops colour and depth; without it the finished dish is flat.
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3
Pour in the Shaoxing wine; it will hiss and reduce in seconds. Add the soy sauce, dark soy sauce, rock sugar, star anise, five-spice powder, and ginger. Pour in the water to just cover the trotters. Bring to a gentle simmer, stirring until the rock sugar has fully dissolved — the liquid should be a deep reddish-brown from the moment the sugar melts.
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4
This is where the dish lives or dies: reduce the heat to the lowest possible setting, cover tightly, and braise for 2 to 3 hours without allowing the liquid to rise above a bare tremble. An aggressive boil will break the skin apart before the collagen has time to convert; a slow, patient heat melts the collagen into the sauce while holding the skin intact. At 2 hours, test a piece — the skin should yield to the lightest pressure of a fingernail, pulling away from the bone without resistance, and feel distinctly slippery between the fingers.
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5
Remove the lid and raise the heat slightly. Reduce the braising liquid, spooning it continuously over the trotters, until it coats the back of a spoon thickly and clings to the skin in a glossy, lacquer-like layer.
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6
Remove from the heat and allow the trotters to cool in the braising liquid. The residual gelatin will set the sauce to a coating consistency around each piece. Serve at this stage — or refrigerate and serve cold, when the sauce will have set to a firm, sliceable jelly.