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1
Combine the sliced lamb with the egg white, cornstarch, and soy sauce. Mix until every surface is lightly coated. Rest for at least 15 minutes. The marinade should feel slick and just adhesive — not pooling at the base of the bowl.
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2
Heat the wok over the highest possible flame until it begins to smoke. Add oil and slide in the julienned onion. Toss continuously until the edges caramelise and the kitchen fills with a sweet roasted smell.
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3
Push the onion to the wok's rim. Add the whole cumin seeds and dried Xinjiang chillies directly to the centre of the wok. This is where the dish lives or dies: the cumin must pop, crackle, and take on a visible char at the edges — released smoke will be dense and spiced — before anything else enters the pan. Insufficient heat here means the lamb will steam rather than sear and the characteristic smoky-spiced crust will not form.
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4
Add the velveted lamb in a single layer if the wok allows. Sear without stirring for 30 seconds, then toss vigorously. The lamb is done when each slice carries a dry, lightly charred crust on its surface and has just lost its raw pink colour — stop before it tightens and turns grey.
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5
Scatter the Xinjiang chilli flakes over the wok and toss once. Remove from the heat. Add the coriander leaves and fold them in off the flame — residual heat alone should wilt them. The leaves must remain bright green and retain their fresh lift.