Step 1
In a large bowl, stir together the Shaoxing wine, light soy sauce, sugar, oyster sauce, dark soy sauce, salt, and white pepper. Add the chicken and toss to coat. Cover and refrigerate for at least 30 minutes and up to 1 hour.
Step 2
Place a large wok over high heat. When it starts to smoke slightly, turn the heat to low, add the oil, and swirl to evenly coat. Add the garlic, three-quarters of the scallions, and the ginger, and cook, stirring frequently, until fragrant, about 3 minutes. Turn the heat to medium-high, add the chicken in a single layer (reserve the marinade), and cook, undisturbed, until the chicken is lightly browned, about 2 minutes. Flip and continue cooking until lightly browned on the other side, about 2 minutes more. Turn the heat to medium, stir in the reserved marinade, cover, and simmer until the chicken is tender, about 20 minutes.
Step 3
Meanwhile, in a small bowl, stir together the cornstarch and 1 tablespoon of water. Turn the heat to high, add the cornstarch slurry to the wok, and cook, stirring frequently, until the sauce has thickened, about 5 minutes. Stir in the remaining scallion, then transfer to a platter and serve warm.