Stir fry sauce:
Cut the beef into bite-sized pieces. (To create a tender cut, make sure you cut against the grain and slice it on an angle.) Transfer to a mixing bowl.
Add the soy sauce, Shaoxing wine, white pepper, cornstarch, baking soda, and oil. Give it a good massage. Cover and marinate in the fridge for 10 minutes.
Prep vegetables: Thinly slice the green onion. Finely chop the garlic cloves. Grate a small knob of ginger, about 2 teaspoons. Cut the onion and bell peppers into squares.
Make the stir-fry sauce: Combine all the sauce ingredients in a small container and mix well.
To a wok (or pan), add 1 tablespoon of oil. Heat it over high heat. Once it gets hot, add the marinated beef in a single layer. Sear the beef for 1 minute or nicely browned on the bottom. Flip and cook the other side for 1 to 2 minutes or until the beef is just cooked. Remove from the wok and set it aside.
To the same wok, add 1 tablespoon of oil. Heat it over high heat. Once heated, add the onions. Spread them out, and let them sit for 1 minute or until nice and charred.
Add the green onion, garlic, and ginger. Saute for 30 seconds or until fragrant. Add the bell peppers. Stir-fry for 1 to 2 minutes or until they are cooked but still have some crunch.
Add the cooked beef. Give the sauce a quick stir and add it to the wok. Toss everything together for 1 minute or until the beef is shiny and evenly coated with the sauce.
Turn the heat off. Add 1 teaspoon of sesame oil and ½ teaspoon of black pepper. (If you want to add more heat, you can add up to 1 teaspoon.) Give it a final mix. Serve with hot rice. Enjoy!