In a large bowl, combine beef strips with oil, soy sauce, and cornstarch. Set aside for 30 minutes.
In a medium bowl, combine chicken stock, remaining 4 teaspoons light soy sauce, dark soy sauce, sesame oil, salt, and sugar.
In a separate small bow or measuring cup, combine the remaining 2 tablespoons cornstarch with 2 tablespoons of water to make a slurry. Set aside.
Heat 2 tablespoons of oil in a wok or large skillet over medium-high heat. Add the beef and cook for 1-2 minutes, stir and quickly cook for an additional 20-30 seconds. Remove from the pan and set aside. Add more oil if needed. Stir in asparagus, garlic, and scallions and sauté for 1 minute. Add the mirin, stir, and cook for 1 minute. Add the beef back into the pan with the veggies; pour the soy sauce mixture and bring to a boil. Stir in the cornstarch slurry and cook for 1 to 2 minutes or until thickened. Remove the pan from the heat.
Garnish with more scallions and sesame seeds. Enjoy!
