Cantonese Beef with Pepper Sauce
1. Cut beef into strips and toss beef with vinegar and set aside to marinate for 10 minutes. Combine the oyster sauce, soy sauce, sugar and stock in a bowl.
2. Heat a little oil in a wok and stir-fry beef in two batches for 5 minutes to brown. Return all beef to the wok, add garlic and crushed black pepper, and stir-fry for 1 minute more.
3. Add sauce and stock, then bring to the boil. Toss and stir-fry for 2 to 3 minutes, then serve. Garnish with sliced chilli if desired.