The key to mastering classic Chinese food flavor at home is a technique known as velveting, which is essentially an egg white, cornstarch and sherry marinade that preserves the moisture of the meat. This recipe includes an abridged version of velveting that still delivers tender slices of steak bathed in a rich reduction of soy sauce and brown sugar.
1/2 teaspoon minced fresh ginger
1 tablespoon minced garlic
1/2 cup low sodium soy sauce
1/2 cup water
2/3 cup dark brown sugar
1 (1-pound) flank steak
1/4 cup cornstarch
3 scallions (green parts only), sliced into 1-inch pieces
Heat 2 teaspoons vegetable oil in a small saucepot over medium-low heat. Add the ginger and garlic and sauté until golden, about 2 minutes. Add the soy sauce and water, stirring to combine.
Stir in the brown sugar and increase the heat to medium. Bring the sauce to a boil for 3 minutes. Remove the sauce from the heat and set aside.
Slice the flank steak against the grain into 1/4-inch pieces, then toss it with the cornstarch. Place the coated pieces of steak in a sieve and shake off any excess cornstarch. Allow the steak to sit 10 for minutes.
Place a large sauté pan or wok over medium-high heat and add 1/2 cup vegetable oil. Once the oil is hot (but not smoking), add the beef to the pan and sauté for 2 minutes until it is seared on all sides but barely cooked in the center. Remove the steak from the pan with a slotted spoon and transfer it onto a paper towel-lined plate. Pour any excess oil out of the wok.
Place the sauté pan back over medium heat. Add the prepared sauce to the hot pan (it should come to a boil almost immediately), then add the reserved steak and cook at a boil, stirring constantly, 2 minutes. Add the sliced scallions, stirring to combine.
Transfer steak and scallions with a slotted spoon to a plate and serve.
The key to cooking with cornstarch is that it must come to a boil in order to serve its purpose as a thickener.