Slice steak against the grain into 2" long pieces about 1/4" thick. Place the steak in a bowl and add baking soda, light soy sauce, sesame oil, white pepper, cornstarch, and avocado oil. Mix well and marinate for 20 minutes.
In a small bowl, mix together oyster sauce, shaoxing wine, light soy sauce, dark soy sauce, coarse black pepper, sugar, beef stock, msg (optional), and cornstarch. Mix until the sauce is thoroughly combined.
Heat 4 tbsp of oil in a large wok or pan over high heat until just smoking and cook half of the beef for 2-3 minutes until golden brown, then remove the beef to a plate. Bring the oil to slightly smoking again, then cook the remaining beef the same way. Remove the beef and oil, leaving 2 tbsp of oil in the pan.
Over medium high heat, add the minced garlic and stir fry for 30 seconds. Add the sliced onions and bell pepper and cook for 1-2 minutes over high heat or until the vegetables are slightly softened but still crisp.
Add the cooked beef back to the pan. Mix the sauce a final time to mix any cornstarch that has stuck to the bottom of the bowl, then pour the sauce along the edge of the pan.
Mix and toss the sauce and ingredients for another 1-2 minutes over high heat until the sauce has thickened. Serve with white rice and enjoy!
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Notes
Slice Steak Against the Grain: Follow the lines (which is the muscle fibers) in the raw steak and cut against them. Slicing beef against the grain is an easy way to get tender Black Pepper Beef - cutting the fibers of the muscle means they won't get tough when cooked.Store leftover Black Pepper Beef in the refrigerator in an airtight container for up to 3-4 days. The sauce tastes even better the next day, making this a great meal prep option!Because Black Pepper Beef is not coated in a batter, you won't have to worry about trying to restore the crispy texture of the dish - I recommend reheating this in the microwave or in a hot pan/wok for a couple minutes (add a little bit of water if you want to loosen up any pieces that may have stuck together in the refrigerator).