Slice the steak against the grain into very thin slices.
Combine the soy sauce, sherry, and cornstarch and pour this mixture over the steak.
Marinate the meat for 15 minutes.
While the meat is marinating, slice the broccoli at a diagonal and mince garlic and ginger.
Heat a wok or large frying pan for 30 seconds, add oil, wait about 20 seconds, and add minced garlic and ginger root. Fry over high heat, stirring constantly for about 20 seconds more, then add the beef.
Stir-fry, stirring constantly, for about 1 minute. Add broccoli and stir-fry for another 4 to 6 minutes, until the broccoli is cooked but still crisp and still dark green.