Using a mortar and pestle or a rolling pin, coarsely crush the whole black peppercorns until fragrant and slightly uneven in size.

In a medium bowl, whisk together the oyster sauce, Shaoxing wine, soy sauce, toasted sesame oil, most of the crushed black pepper, and potato starch until smooth and well combined.

Take the beef tenderloin and cut it into bite-sized cubes, then coat the cubes in the prepared sauce and let the beef marinate for about 10 minutes.

Place a non-stick frying pan over medium-high heat and add a drizzle of vegetable oil, heating until it shimmers.

Add the marinated beef in a single layer, searing for about 2-3 minutes on one side until it develops a brown crust, then flip and cook for another 2 minutes.

Introduce the chopped onion, sliced bell pepper, and minced garlic to the pan and stir-fry for about 3-4 minutes.

Pour the remaining marinade over the beef and vegetables, stir-frying for an additional 1-2 minutes until the sauce thickens.

Transfer the Black Pepper Beef to a serving plate, sprinkle the remaining crushed black pepper on top, and serve immediately over steamed rice or noodles.