In a medium-sized bowl, whisk together the oyster sauce, sherry, sesame oil, soy sauce, sugar, and cornstarch until the sugar fully dissolves. Place the beef strips in a shallow dish and pour the marinade over them. Stir until the meat is thoroughly coated, then cover and refrigerate for at least 30 minutes to let the flavors meld.

Heat a wok or large skillet over medium-high heat and add the vegetable oil. Once the oil is hot, toss in the slice of ginger and the smashed garlic clove. Allow them to sizzle for about a minute, releasing their aromatic flavors into the oil, then remove and discard.

Add the broccoli florets to the infused oil and stir-fry, tossing frequently, until they turn bright green and are just tender, about 5 to 7 minutes. Transfer the cooked broccoli to a plate and set it aside.

If needed, add a little more vegetable oil to the wok. Add the marinated beef along with the marinade and stir-fry until the sauce thickens, takes on a glossy sheen, and the beef is cooked through, approximately 5 minutes.

Return the broccoli to the wok, combining it with the beef and sauce. Stir-fry for an additional 3 minutes until everything is evenly heated and well-coated with the sauce.

Serve hot, paired with steamed rice or noodles, and enjoy this flavorful and satisfying dish.