Set aside 3/4 tsp/4 mL of the cornstarch. In large bowl, whisk together remaining cornstarch, flour, pepper and salt.

In separate bowl, whisk egg white with 2 tbsp/30 mL water.

Coat fish with cornstarch mixture, then dip in egg-white mixture, letting excess drip off. Coat again with cornstarch mixture.

Into large skillet over medium-high heat, pour oil to 1/2-inch/1 cm depth; heat oil until thermometer registers 350F/180C or small bubbles immediately form around edge of dry wooden spoon dipped into oil. Add salmon; fry, turning once halfway through, until golden, crispy and just translucent at centre of thickest part, 6 to 8 minutes.

With slotted spatula, transfer to paper towel and drain well; transfer to warmed platter and keep warm.

Mix reserved cornstarch with stock until paste. Stir in vinegar, soy sauce and sugar until sugar is dissolved; set aside.

From skillet, pour off all but 2 tbsp/30 mL of the oil; over high heat, stir-fry garlic, ginger and hot pepper until fragrant, about 30 seconds. Add wine, then onions; fry until onions begin to wilt, 10 to 20 seconds. Add stock mixture and bring to boil; boil for 30 seconds and pour over salmon. Garnish with coriander, if desired.

Makes 4 servings.