1. Stir the cornstarch, broth, soy sauce, brown sugar and garlic powder in a small bowl until the mixture is smooth.
2. Stir-fry the beef in a 10-inch nonstick skillet over medium-high heat until it's well browned, stirring often. Pour off any fat.
3. Add the broccoli to the skillet and cook for 1 minute. Stir in the cornstarch mixture. Cook and stir until the mixture boils and thickens. Serve the beef mixture over the rice.
Ingredient Note: To make slicing easier, freeze the beef for 1 hour before slicing.