Marinate the Beef
Combine all beef marinade ingredients (steak strips, baking soda, soy sauce, sesame oil, white pepper, and cornstarch) in a bowl. Mix thoroughly to ensure each strip is evenly coated. The baking soda helps tenderize the meat while the cornstarch will give the beef a velvety texture. Cover with plastic wrap and refrigerate for 20 minutes to allow the flavors to penetrate the meat.
Prepare the Sauce
In a small bowl, mix together all sauce ingredients (oyster sauce, Sichuan peppercorn, black pepper, Shaoxing wine, both soy sauces, sugar, and cornstarch) until well combined. The cornstarch will help thicken the sauce when cooked. Set aside until needed. This can be prepared while the beef is marinating to save time.
Cook the Beef
Heat vegetable oil in a wok or large skillet over high heat until it begins to shimmer. Add half of the marinated beef in a single layer and cook for 2-3 minutes until the exterior is golden brown but not overcooked. Remove to a clean plate and repeat with the remaining beef. Cooking in batches prevents overcrowding, which would steam rather than sear the meat. Drain excess oil, leaving about 2 tablespoons in the wok.
Sauté the Aromatics and Vegetables
Reduce heat to medium-high. Add minced garlic to the wok and stir-fry for about 30 seconds until fragrant but not browned. Add the onion and bell pepper pieces and continue to stir-fry for about a minute until they begin to soften but still maintain some crispness. The vegetables should be tender-crisp rather than fully soft.
Combine and Finish
Return the cooked beef to the wok and immediately add the prepared black pepper sauce. Toss everything together continuously until the ingredients are well combined and the sauce has thickened, coating all components evenly. This should take about 1-2 minutes. For an extra dimension of flavor, drizzle with a little additional sesame oil just before removing from heat.
Serve
Transfer to a serving plate and serve immediately over steamed rice while hot and fragrant. The dish is best enjoyed fresh from the wok when all the flavors are at their peak and the sauce is glossy.