Spicy Mongolian Beef

Toast sesame seeds in a dry skillet over medium heat until golden, 1 to 2 minutes; set aside.

Mix 1 tablespoon soy sauce, 1 tablespoon cornstarch, and garlic in a medium bowl. Add beef strips and toss to coat. Let stand for at least 10 minutes.

Mix water, remaining 2 tablespoons soy sauce, remaining 2 ½ teaspoons cornstarch, sugar, toasted sesame seeds, and red pepper flakes in a small bowl; set aside.

Heat 1 tablespoon oil in a wok or large skillet over high heat. Add beef and cook, stirring, until browned, about 1 minute; transfer to a plate.

Heat remaining 1 tablespoon oil in the same pan. Add carrots and white parts of green onions; stir-fry for 2 minutes. Add green parts of onions and stir-fry for 1 minute.

Stir the sauce mixture again, then add it to the pan with the beef. Cook, stirring, until the sauce boils and thickens and the beef is cooked through, 1 to 2 minutes.