Using a sharp knife, carefully slice the flank steak across the grain into thin slices, about ¼-inch thick. (For easier slicing, freeze the meat for about 10 minute before slicing). Add to a mixing bowl and season on all sides with kosher salt. Toss with about 2-3 Tablespoons Hong Kong sauce.\nPreheat a large skillet or wok to high heat and coat with a drizzle of cooking oil. Once the oil is very hot, add in the steak (you should hear it sizzle). Sauté until the meat is deeply caramelized on both sides, about 3-5 minutes. Transfer to a plate to rest.\nAdd another Tablespoon of oil to the skillet used to cook the beef and once hot, add in the shallot, broccoli and a pinch of salt. Sauté until the broccoli is tender and beginning to brown, about 4-5 minutes. Return beef to the pan along with about 1\/3 cup Hong Kong sauce. Bring to a boil and continue stir frying for about 1-2 minutes more, allowing the sauce to thicken and flavors to meld. \nToss with toasted sesame seeds and transfer to a serving bowl. Serve warm.