Steep the bean curd in hot water for about 15 minutes. Drain, handling with care to keep each cake whole. Cut each cake into 3 slices. Lay the rectangular slices flat on paper towels to absorb excess water.
Prepare the stuffing. Put the minced haddock in a bowl. Add the salt and stir vigorously in the same direction for about 1 minute, until gelatinous in texture. Sprinkle with cornstarch, add the egg white, then stir until the fish mixture becomes one lump. Add the pepper, ginger, and ham. Stir to mix well.
Using a small pointed knife, cut a small rectangle in the center of each slice of bean curd, about ⅔ x 1inch and ¼inch deep. Gently scrape away this layer of bean curd and discard.
Into each hollow, put about 1½teaspoons stuffing and level the stuffing with the surface of the rest of the bean curd.
Mix together the sauce ingredients and set aside.
Heat the wok over a high heat until smoke rises. Add 4tablespoons of the oil and swirl it around. Add the ginger, let sizzle until brown, then remove, and discard. Add 6slices stuffed bean curd, one at a time, stuffing side down, into the oil. Fry over a moderate heat for about 3 minutes, until golden in color. Slipping the wok scoop or metal spatula underneath the bean curd, carefully turn the slices over, one by one. Fry the other side for about 2 minutes. Remove to a serving dish, leaving behind in the wok as much oil as possible.
Add 1tablespoon oil and reheat over a high heat. Add another 6slices bean curd and fry as before. Repeat until all are done.
Lower the heat. Add the well-stirred sauce, and stir until it comes to a boil and thickens. Spoon onto the bean curd. Sprinkle on the sesame oil and serve hot.