Trim the beef of any fat and cut in thin strips.
Blend 1 tsp (5 ml) of oil with the soya, sherry, garlic and ginger and pour over the beef.
Marinate 2 hours.
Slice the mushrooms.
Heat the remaining oil in a wok.
Quickly fry the beef, undrained, with the mushrooms.
Stir in the tomato paste and cook 1 minute longer.