How to Make It
Combine beef strips, egg, salt, and 1 tablespoon of the oil in a medium bowl. Toss well, and let stand 15 minutes.
Whisk together beef stock, sugar, vinegar, mirin, soy sauce, chili oil, bean sauce, and 1 tablespoon of the cornstarch in a small bowl; set aside.
Drain and discard liquid from beef strips. Add remaining 1/2 cup cornstarch, and toss to coat.
Heat remaining 1/3 cup vegetable oil in a large nonstick skillet or wok over medium-high. Add coated beef strips to skillet in a single layer; cook, undisturbed, until golden brown, 2 to 3 minutes. Flip and brown on other side, 1 to 2 minutes. Transfer beef to a plate.
Add garlic scapes, de árbol chiles, bell peppers, and onion to skillet; cook, stirring often for 2 minutes. Add ginger and garlic; cook, stirring often, until fragrant, 1 minute. Stir beef stock mixture into vegetable mixture; cook, stirring often, until sauce begins to thicken, about 3 minutes. Add beef to mixture, and stir to combine. Serve immediately over rice, and sprinkle with toasted sesame seeds.