In a bowl, toss the sliced flank steak with soy sauce, Shaoxing wine, and cornstarch. Let sit for 10 minutes while you prep the other ingredients.
In a small bowl, whisk together all sauce ingredients until sugar dissolves. Set near the stove.
Heat a wok or large skillet over high heat until smoking. Add 1 tbsp oil, then the marinated beef in a single layer. Let sear undisturbed for 1 minute, then stir-fry until just browned and internal temperature reaches 145°F (63°C). Remove to a plate.
Return wok to heat, add remaining oil. Toss in dried chilies and Sichuan peppercorns; stir 15 seconds until fragrant. Add garlic, ginger, and bell pepper, stir-fry 1 minute. Add white parts of scallions, cook 30 seconds.
Return beef to the wok along with the sauce mixture and peanuts. Stir-fry until sauce thickens and coats everything, about 1 minute. Toss in green scallion parts, then remove from heat immediately.