In a mixing bowl, combine minced garlic, sesame oil, soy sauce, oyster sauce, Chinese white rice vinegar, and a spoonful of cornstarch to create a marinade. Add the thinly sliced beef, ensuring each piece is well coated. Let it marinate for about 10 minutes.

Bring a pot of water to a rolling boil over high heat. Add the udon noodles and cook them for 1-2 minutes, or until they are tender yet still chewy. Drain the noodles in a colander and rinse briefly under cold water. Set the cooked noodles aside.

In a large wok, heat a tablespoon of oil over medium-high heat. Add minced garlic and sliced white onion, stir-frying for about 2 minutes. Next, add the chopped Chinese cabbage and season with a pinch of salt and sugar. Cook for another 2-3 minutes until the cabbage wilts down, then transfer to a plate.

Using the same wok, add the marinated beef along with the marinade. Spread the beef in an even layer and let it sear for about 2-3 minutes. Stir occasionally until the beef is nicely browned and slightly caramelized.

In a small bowl, mix the remaining marinade ingredients: dark soy sauce, freshly ground black pepper, and water. Pour this mixture into the wok with the cooked beef, stirring gently. Allow the sauce to simmer for 1-2 minutes.

Add the cooked udon noodles and the sautéed vegetables back into the wok, tossing everything together gently. Cook for an additional minute. Your Black Pepper Beef Udon is now ready to serve!