Slice the steak into thin strips. (About 1/ 8 inch)
Place the steak strips into a disposable plastic bag or reusable container; then add the soy sauce, sherry, and cornstarch; mix thoroughly to combine. (if you us a plastic bag-seal the bag and work the mixture from the outside with your hands to combine) Marinate for 15-30 minutes.
In a large skillet or wok add the oil, minced garlic, and ginger. Cook on medium high heat for about 20 seconds.(This cooks fast so be careful not to overcook)
Add the beef mixture, stirring constantly until beef is no longer pink inside. Add the broccoli florets and stir fry for an additional 5 minutes. Broccoli will be dark green and crisp.