In a small bowl combine, baking soda, cornstarch, soy sauce, oyster sauce and oil. Slice the beef against the grain in little pieces. Then mix with the sauce. Cover and let it rest in the fridge about an hour or preferably overnight for velvety meat.
In another bowl combine the soy sauce, sherry,water, chicken stock, oyster sauce, cornstarch, and brown sugar. Set aside.
Heat up the Wok with about 1 tablespoon of oil, and then add meat let it rest for about 30 seconds before stirring. Cook for 2 minutes or until beef reaches desired doneness; remove and keep warm.
Stir fry the broccoli and onion for two minutes, then add garlic, ginger and continue stirring for another 2 -3 minutes.
Add the combined sauce, cook and stir for about 2 minutes, followed by the beef.
Remove and serve over rice.