In a medium sized bowl, toss the beef slices in salt, pepper and cornstarch. Set aside.
1 pound flank steak, ¼ cup cornstarch, 1 teaspoon kosher salt, ½ teaspoon black pepper
In a small saucepan, whisk together brown sugar, soy sauce, chicken broth, half the ginger and garlic, and simmer over medium heat until reduced by ¼, about 15 minutes.
½ cup soy sauce, ¼ cup chicken broth, 4 garlic cloves, ¼ cup dark brown sugar, 2 teaspoon ginger
In a large skillet, wok, or saute pan, heat vegetable oil over medium-high heat and place steak pieces in one layer in batches. Cook for 2 minutes on one side then another minute on the other, the beef should have a brown crispy crust on each piece. Using an Asian spider, scoop each batch up onto a plate lined with paper towels to absorb excess oil.
½ cup vegetable oil
After all batches are done, discard the excess oil from the wok, leaving about 2 tablespoon of oil or so in the pan. Add the rest of the garlic and ginger, half of the green scallions, the sambal oelek (or red pepper flakes or sriracha), into the oil and stir. Let that sizzle for about 2 minutes, until fragrant.
2 teaspoon ginger, 4 garlic cloves, 2 green onions, 1 teaspoon sambal oelek
Add our soy sauce mixture into the wok with sesame oil and let the sauce reduce more for 5 minutes over medium heat stirring occasionally. Once reduced into a sticky sauce, add the sesame oil and toss the beef in. Cook for another minute to coat them.
2 teaspoon sesame oil
Toss in sesame seeds and the reserved sliced green onion then serve immediately with white rice and vegetables, if desired.
sesame seeds, white rice, 2 green onions