Marinate beef with soy sauce, sesame oil, black pepper, and potato starch.
Mix stir-fry sauce ingredients: oyster sauce, soy sauce, sweet soy sauce, dark soy sauce, black vinegar, and water.
If using dried flat rice noodles, cook according to package instructions.
Stir-fry minced garlic, minced ginger, and sliced shallots.
Add marinated beef and cook.
Add flat rice noodles, Chinese chives, and bean sprouts.
Pour in the stir-fry sauce mixture and toss to combine.
