Cut the beef tenderloin into 2cm cubes and marinate with seasoning, potato flour and a little cooking oil. For the sauce: heat up the wok; cook the butter and garlic until soft and fragrant.

Coat the diced beef in the plain flour Scoop out the softened mushroom, then add the beef and cook it over a high heat until browned all over - you might need to do this in batches Add the onions ...