To season the shrimp, on a plate, combine the shrimp, salt, white pepper, and cornstarch. Mix well until evenly coated.
To prepare the ingredients, slice the onion and scallions, and mince the garlic.
To make the stir-fry sauce, in a bowl, whisk together the soy sauce, dark soy sauce, oyster sauce, and chicken stock.
To boil the rice noodles, in a pot over high heat, bring water to a boil. Add the rice noodles and cook for about 3 minutes, just until softened. Immediately transfer the noodles to cold water to stop the cooking process. Drain well and set aside.
To stir-fry the shrimp, in a wok over high heat, add 1 tablespoon of cooking oil. Add the shrimp and garlic and stir-fry for about 1 minute, until lightly pink. Remove from the wok and set aside.
To stir-fry the onion, in the wok over high heat, add 1 tablespoon of cooking oil. Add the onion and stir-fry for about 1 minute, until slightly softened. Remove and set aside.
To stir-fry the shrimp chow fun, in the wok over high heat, add the remaining 1 tablespoon of cooking oil. Add the rice noodles and stir-fry until heated through. Return the onion and pour in the sauce. Toss for about 1 minute until the noodles absorb the sauce. Add the shrimp back in, along with the bean sprouts and scallions. Give everything a quick toss and remove from the heat.