In a bowl, mix flank steak with Thai black soy sauce, vegetable oil, and cornstarch until completely coated. Set aside.
In another bowl, combine oyster sauce, sugar, Thai soy sauce, Thai black soy sauce, fish sauce, and white pepper. Stir well to create a flavorful sauce.
Ensure fresh rice noodles are at room temperature. If cold, quickly rinse under hot tap water to avoid clumping during stir-frying. Shake off excess water and set aside.
For best results, use fresh wide rice noodles. Homemade rice noodles are also an option. If using dried noodles, halve the amount and undercook slightly. Toss with oil after draining to prevent sticking.
Heat the wok on high until it smokes slightly. Spread 1 tablespoon of oil evenly. Sear the beef until 80% cooked, then return it to the marinade bowl.
Add another tablespoon of oil to the wok. Stir in garlic, then quickly add Chinese broccoli, stir-frying for 20 seconds.
Spread room temperature noodles in the wok. Pour the sauce over the noodles and gently mix with a scooping motion for about 20 seconds. Add the beef back to the wok.
Push the mixture to one side, add a tablespoon of oil, and pour in beaten eggs. Scramble for a few seconds, breaking them into smaller pieces.
Stir-fry the mixture until the noodles heat up evenly. Scrape the wok bottom to prevent sticking. Let the noodles caramelize slightly for that restaurant-style flavor.
Continue cooking for 1 to 2 minutes until noodles are heated through. Serve hot and enjoy with Homemade Chili Oil or Chiu Chow Sauce on the side!