Put the steak in a bowl, add all the marinade ingredients and mix to coat. Leave to marinate for at least 10 minutes (the marinade can be covered and kept in the fridge up to a day ahead).
Cook the asparagus spears in a wok or saucepan of boiling water for 2 minutes, then drain and rinse under cold water straight away to stop them cooking – you want them to remain crunchy.
Heat the vegetable oil in a wok or frying pan (skillet) over a high heat, add the marinated beef strips and fry for a couple of minutes – do not overcook them (pink is fine). Remove from the wok or pan.
Now make the black pepper sauce. Add the vegetable oil to the wok or frying pan (you don’t need to clean it), place over a high heat, then add the garlic and fry for about 30 seconds, just until it starts to release its aromas.
Add the white pepper, black pepper, soy sauce, Shaoxing wine, oyster sauce and sesame oil and simmer for a couple of minutes, then add the stock until the sauce reaches your desired thickness.
Taste and season as required. Add water or extra stock if you want more sauce, or if you want it thicker add 1 teaspoon of cornflour paste at a time and allow it to come to the boil after each addition. Return the beef and asparagus to the wok or frying pan and serve.