1 lb. trimmed, boneless sirloin steak, cut 1/2 inch thick
1 tsp. cornstarch
2 tbsp. soy sauce, preferably dark
2 tbsp. dry sherry
1/2 c. peanut oil
2 1/2 oz. fresh ginger, peeled, cut into fine 2-inch shreds (about 1/2 c.)
1 bunch watercress, tough stems removed

Slice the steak crosswise on the diagonal into very thin strips, about 2 x 1/2 x 1/4 inch. Place in a bowl and sprinkle with the cornstarch. Toss to coat evenly. Stir in the soy sauce and sherry. Set aside for 5 minutes.

In a wok or large skillet, heat the oil--a piece of meat should sizzle loudly on contact. Add the meat, reserving the marinade in the bowl. Stir-fry over high heat until the meat loses most of its pinkness, about 1 minute. With a slotted spoon, transfer to paper towels to drain.

Pour off all but 1 tablespoon oil from the wok. Add the ginger and stir-fry over high heat for 15 seconds. Add the watercress and the cooked steam and stir-fry for 5 seconds. Pour in the reserved marinade and toss for 10 seconds. Transfer the mixture to a warmed platter. Serve hot with plain boiled rice.