Slice the flank steak thinly against the grain. Combine the steak with 1 tablespoon soy sauce, 1 tablespoon peanut oil, 1 tablespoon cornstarch, and 1/2 teaspoon baking soda if using. Mix well and marinate for at least 15 minutes. In a bowl, whisk together chicken stock, Shaoxing wine, 2 tablespoons soy sauce, dark soy sauce, brown sugar, and 1 tablespoon cornstarch. Heat 1 tablespoon peanut oil in a wok or large skillet over medium-high heat. Add the marinated beef and stir-fry until browned but not fully cooked, about 2-3 minutes. Remove beef from the wok and set aside. In the same wok, add garlic and ginger and stir-fry briefly until fragrant. Add broccoli florets and stir-fry for 3-4 minutes until bright green and tender-crisp. Return the beef to the wok. Pour in the sauce mixture and stir continuously until the sauce thickens and coats the beef and broccoli evenly. Remove from heat and serve immediately with steamed rice or noodles.