Prepare the shan yao: Peel and cut the shan yao into rounds about 1cm thick — the smaller and more even, the faster they cook. Bring a pot of water to a boil and cook the shan yao for about 2-3 minutes. Drain well and pat dry. Toss in a thin, even layer of cornstarch to coat (about 2 tablespoons).
Double fry: Heat the oil to 350°F (180°C). Fry the shan yao until lightly golden, then remove and drain. Increase the oil temperature to 375°F (190°C), then fry again until crisp and golden. Remove and drain on paper-lined plate.
Mix the sauce: In a small bowl, combine the salt, sugar, Chinese black vinegar, soy sauce, and dark soy sauce. Mix the 1 teaspoon cornstarch with 5 teaspoons of water to make a slurry and stir it into the sauce. Set aside.
Stir-fry aromatics: Heat a wok over medium heat with ½ tablespoons of oil. Add the ginger, hua jiao, and dried chilies. Stir-fry gently until fragrant, keeping the heat at medium-low — hua jiao burns easily and turns bitter.
Toss and finish: Add the carrot and wo sun and stir-fry for about a minute. Add the fried shan yao and toss to combine. Swirl in the sauce and quickly toss until every piece is evenly coated. Add the roasted peanuts, give it one final toss, and serve immediately.