Bring a large pot of lightly salted water to a boil. Add the Chinese broccoli and cook uncovered until just tender, about 4 minutes. Drain and set aside.
Meanwhile, whisk the sugar, cornstarch, soy sauce, vinegar, sesame oil, hoisin sauce, ginger, and garlic together in a small saucepan over medium heat until thickened and no longer cloudy, 5 to 7 minutes. Toss the broccoli in the sauce and serve.