To make the sauce. Combine all ingredients in a glass jar.In a large skillet, combine the oil, chicken, cornstarch, pepper, and chili flakes. Cook over medium heat, breaking up the meat as it cooks until browned, about 5 minutes. Add the butter and garlic. Cook 2 minutes, until the butter browns and the chicken gets crispy.Pour over the sauce. Cook until the sauce thickens slightly. Then, add the broccoli. Cook another 2-5 minutes. Remove from the heat.Serve the chicken, broccoli, and remaining sauce over bowls of rice. Top with sesame seeds and green onion. Enjoy!