Pat dry the salmon filets with kitchen paper to remove any moisture on the surface.
In a microwave-safe bowl, mix all the ingredients for the sauce until well incorporated. Microwave for 20 seconds so that the sugar is fully dissolved.
Pour the sauce into a roasting pan/oven dish. With the skin side facing up, lay the salmon filets over the sauce. Leave to marinate for 10 minutes or so.
While waiting, prepare the oven by moving the rack up so that the salmon will be placed about 4 in/10 cm below the top heat element (not closer than that though). Preheat the oven to 425°F/220°C using the broil with fan setting (aka grill with fan).
When the oven is preheated, brush a thin layer of olive oil over the skin, then sprinkle a little fine salt on top (do not overdo it).
Put the pan/dish onto the oven rack. Leave to cook for about 10 minutes until the skin becomes crispy and the flesh is cooked (see note 3 for adjustment). Garnish with chopped scallions and serve immediately.
Video
Notes
1. You may use either Chinese or Japanese white rice vinegar. Alternatively, use cider vinegar as a substitute.2. Shaoxing rice wine can be replaced by dry sherry or white wine.3. Depending on the size of the filets, cooking time varies. Begin checking at 8 minutes. Add more time if necessary. If available, use a meat thermometer to insert into the thickest part of the salmon, it should read above 145°F/63°C.