In a mixing bowl, combine the beaten egg, salt, cold water, and cornstarch. This marinade will help tenderize the steak and create a lovely batter once fried. Add the flank steak slices and ensure they are well-coated. Let it sit for about 20 minutes.

While waiting for the beef, let’s whip up the sauce. In a bowl, combine water, soy sauce, apple cider vinegar, rice vinegar, red pepper flakes, sugar, ketchup, hoisin sauce, oyster sauce, sweet chili sauce, and ginger. Mix well until the sugar dissolves completely; set aside.

Once the beef is marinated, sprinkle cornstarch over it and toss to coat each piece evenly. This will give a beautiful crispy texture once it hits the hot oil.

In a large skillet or wok, heat the peanut oil over medium-high heat. Once it’s hot, carefully add the beef in batches to ensure it fries evenly. Cook each batch for about 3-4 minutes until golden brown. Remove and place on paper towels to absorb excess oil.

Using the same skillet, add a bit more oil if needed, and toss in the minced garlic, onion, and bell peppers. Stir-fry for about 3-4 minutes or until the vegetables start to soften but still maintain a crunch.

Return the fried beef to the skillet with the vegetables. Pour the sauce over everything and stir well to combine. Allow the mixture to simmer for a few minutes so the flavors meld together.

Once everything is heated through, it’s time to serve! Ladle the Beijing Beef onto a bed of jasmine rice or alongside stir-fried vegetables.