Butcher the half duck, cutting through the bone, so that you have pieces about 1 ½-2 inches wide; you can use the neck of the duck, but discard the head, backbone, foot and wing tip (or set them aside for another use, such as making stock). See detailed butchering instructions in story above.
Pour the oil into a wok and heat it on high until it’s very hot; to test the temperature, stick a wooden chopstick in the oil—if it’s hot enough, the chopstick will produce a small cloud of bubbles.
Add the garlic and ginger to the oil and let them fry for 10 seconds, to become fragrant. Carefully add the duck pieces to the oil and fry it, gently stirring, for 1 minute. Add the Shaoxing wine and dried chilies and continue cooking everything, stirring frequently, for another 2 minutes; the duck pieces will have a light gold color.
Pour the oil out of the wok, into a heat-proof bowl (pouring through a strainer or sieve, to catch any solids that try to escape the wok). Return the wok to the heat and add back about 1 tablespoon of the discarded oil.
Add the beer to the wok, bring it to a rolling boil, then let it boil, stirring the duck occasionally, for 2 minutes. (If there’s lots of foam in the wok at this point, you can scoop it out.)
Add the oyster sauce, sesame oil, chili oil, sugar and dark soy sauce to the wok and stir everything together. Let the mixture continue boiling and reducing for 4 minutes.
Add the scallions to the wok and continue to cook everything until they soften, about 2 minutes.
Stir the cornstarch-water mixture, add it to the wok, and let everything simmer and thicken for just a few seconds. Serve the meat and sauce together with rice.
