Mum made a great peppered steak stir-fry last week, and she told me the key was velveting; she had marinated it with some baking powder which apparently makes cheaper cuts of meat more tender.
I then stumbled upon an article describing velveting in asian cooking.
The technique is different, it explains creating a slurry with cornflour.
1 Tbsp. cornstarch 1 Tbsp. soy sauce 1 Tbsp. vegetable or light sesame oil 1 Tbsp. Shaoxing wine or rice vinegar Coat meat (and/or veg) at least 30 mins before cooking. Cook.