On high, heat wok, to around 350-400°F, basically smokin hot.
When the wok is hot, add oil (1 tbsp) and heat to 350-400°F. The oil should be "shimmering" - rippling, but not smoking. If it's smoking, the wok is too hot. Little wisps of smoke is okay.
Saute’ green onion whites and onions for about 1 minute and reserve.
Heat the wok again and add 1 T oil. Once the oil is shimmering, add the noodles.
Move the noodles around the pan gently. DO NOT flip them yet, move the noodles around so parts get crispy. Cook for about 3 minutes moving the noodles carefully.
Turn the top noodles over so the noodles are on the bottom, add 1 T oil along the perimeter of the pan to help develop a nice crisp. Let the noodles cook on this side for another 3 minutes, occasionally prodding and moving the noodles.
The noodles will not stick to the pan if they are not overcooked. Lifting the noodles as you fry helps release moisture.
Add bean sprouts and stir fry for 30-45 seconds. Use tongs or cooking chopsticks to help you move the noodles around. Place the noodles over the sprouts to help cook them. Better to undercook sprouts, you want to retain their crunch!
Add sautéed onion-green onion mixture and mix to incorporate and heat onions. No more than a minute.
Add sauce by pouring it in a steady stream all over the noodles and vegetables. Keep moving and lifting the noodles to coat with sauce and release any extra moisture.
Add sesame oil and continue to mix and separate the noodles for another 1-2 minutes. If the noodles seem to be getting a bit soft, take them off the heat. The oil does not need to cook.
Taste the noodles, season with salt and dark soy if the noodles are not dark enough. Add white pepper if you like.
Garnish julienned green onion shreds. Serve immediately.