2 Tbsp egg white lightly beaten
2 Tbsp + 1 tsp cornstarch
2 Tbsp + 1 tsp Chinese rice wine or sake
1/2 tsp sea salt
1 pound firm fleshed. thick white fish fillets, like flounder, sole, cod or halibut
6 dried wood-ear mushrooms or shiitake mushrooms
1 tsp + 2 tbsp neutral oil
1 tsp oyster sauce
1 tbsp dark soy sauce
1 tbsp low sodium soy sauce
¼ tsp Chinese black vinegar
½ tsp white vinegar
¾ tsp white sugar
1 tbsp sliced scallions, white part only
1 tbsp minced fresh garlic
1 tbsp minced fresh ginger
Pour the egg white into a medium size bowl, then add 1 tbsp + 1 tsp cornstarch, 1 tbsp + 1 tsp rice wine and salt, and whisk until all the cornstarch has dissolved. Use a chefs knife held at a 45 º angle to the cutting surface to slice the fish fillets crosswise into 1/2 inch slices. Add the fish to the cornstarch mixture then carefully toss it to coat the fish and set aside to marinate for 30 - 45 minutes.
Place the mushrooms in a small bowl, then pour hot water over them and allow them to soak for 20 minutes or so, until they are very soft. Remove the mushrooms from the water and dry them, then thinly slice each mushroom (Reserve the mushroom soaking liquid)
Make the sauce. Combine the oyster sauce, the remaining tablespoon of rice wine, soy sauces, vinegars and sugar in a bowl, then whick to combine. Sprinle the remaining tablespoon of cornstarch and whisk to dissolve it into the sauce. Add a tablespoon of the (strained) mushroom soaking liquid and set aside.
Velvet the fish. Fill a wok or large pot with water and bring it to a boil over high heat. Add a teaspoon of oil to the water. Carefully add the fish to the water, piece by piece, working in batches so as not to crowd the pieces. Allow the fish to cook until it has turned opaque, approximately 1 - 2 minutes, depending on the thickness of the fillets.
Using a skimmer or spider, transfer the fish carefully to a platter to rest.
To finish the dish, heat the remaining 2 tablespoons oil in a wok or large skillet set over high heat. When the oil shimmers and is about to smoke, add the scallions, garlic and ginger, and stir fry for 30 seconds or until the mixture is fragrant. Add the mushrooms, and continue to stir-fry for an additional 30 seconds. Stir the sauce mixture,(step 3) and add it to the wok, then cook for 2 - 3 munutes, until it has thickened slightly. If it is too thick, thin it our with some of the strained mushroom-soaking liquid.
Add the fish to the wok, and carefully toss until the flesh is coated.
Transfer to a warm platter and serve immediately.