Start by whisking together the egg, salt, and black pepper in a bowl. Add the thinly sliced flank steak and toss to coat thoroughly with the mixture, then dredge the beef in cornstarch for that crispy crust.

Heat oil in a large skillet or wok over medium-high heat. Working in batches, fry the coated beef pieces for about 3-4 minutes, or until they’re crispy and golden brown. Remove and place on a paper towel to drain any excess oil.

Using the same pan, quickly stir-fry your choice of vegetables (like bell peppers or broccoli) over high heat for about 2-3 minutes. You want them to be vibrant and tender-crisp.

In a separate saucepan, combine the water, soy sauce, hoisin sauce, sugar, rice vinegar, minced garlic, and ginger. Bring to a gentle simmer, allowing the sugars to dissolve and the flavors to meld together for about 5 minutes.

To thicken the sauce, create a slurry by mixing a little cornstarch with water, then slowly stir it into the simmering sauce. Once thickened, toss in the crispy beef and mix well until every piece is coated in that glossy, flavorful sauce.