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1
One to two days before cooking, hold the live or very fresh grass carp in a tank or vessel of clean, changed water. This purging step removes the muddy, intestinal flavour that river fish carry. The fish is ready when it smells cleanly of fresh water and nothing more.
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2
Cut the carp into sections, or leave whole for presentation. Bring a wide pan of lightly salted water to just below a boil — surface shivering, no rolling bubbles. Lower the fish in carefully. Poach for 8–12 minutes. The fish is done when the flesh at the thickest point turns completely opaque and just yields to the touch of a finger without flaking apart. Lift out with care to keep the sections intact.
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3
While the fish poaches, heat the oil in a small saucepan over medium heat. Add the ginger shreds and fry until fragrant. Add the Shaoxing wine and let it hiss and reduce briefly. Add the chicken stock, Chinkiang vinegar, sugar, light soy sauce, and the pinch of salt. Bring to a boil. Pour in the cornstarch slurry in a thin stream, stirring constantly. This is where the dish lives or dies: the finished sauce must be a medium amber-red, flow like a slightly thick glaze, and taste simultaneously sweet, sour, and subtly savoury — with none of the three flavours overpowering any other. Adjust with a few drops more vinegar or a pinch more sugar before it leaves the pan.
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4
Transfer the poached fish to a serving plate. Pour the hot sauce directly over the fish at the table. The sauce should coat the surface in a glossy, even sheet — not pool thinly nor sit in stiff clots.