Rinse the snapper, pat them dry, and use a small sharp knife to puncture and cut slits in them 1 inch apart on both sides of each fish.
To make the marinade, combine the onions, ginger, cilantro, garlic, salt, pepper, orange juice, 1/2 cup of the oil, and 1 tablespoon Essence in a small bowl. Place the fish side by side in a glass dish large enough to hold them flat. Pour the marinade over the fish, turning to coat both sides. Let marinate for 15 minutes at room temperature.
In a large, shallow bowl, combine the cornstarch with the remaining 2 teaspoons of Essence. Drain the fish from the marinade and one at a time, dredge in the cornstarch to lightly coat both sides, shaking to remove any excess.
Heat a large wok over high heat until very hot. Add 1 tablespoon of the oil and 3 tablespoons of the marinade to the skillet. Add one fish and sear for 2 minutes. Turn, drizzle with 1 tablespoon of the oil, and sear until golden, 1 to 2 minutes. Add more of the marinade and cook until cooked through.
To serve, cut the head from each fish, make a long incision along the top edge and the bottom, and loosen the fish horizontally from the central bone or backbone.
Place one half snapper on each of 4 plates, removing the central bone, and spoon 1/4 cup of the Ginger Sake Sauce over each.
Yield: 4 main-course servings