Slice the beef against the grain in little pieces. Then mix with cornstarch, baking soda and black pepper.
Remove from cornstarch, shake off and let it rest for about 10 minutes.
Heat up the wok with about ¼ -1/2 cup oil,, then add meat; let it rest for about 30 seconds before stirring. Cook for 2 minutes or until beef reaches desired doneness - it should barely cook in the center, stir the meat around a little so that it cooks evenly.
Remove, transfer beef to a plate and keep warm.
Add ab with about 1 tablespoon of oil to the wok, add ginger and garlic sauté for about a minute making sure the garlic does not burn.
In a small bowl combine soy sauce , dark brown sugar and water .
Add mixture to the wok , bring to a boil and stir for about a minute .
Next, add beef to the wok . Bring to a boil, continually stirring for about 2 minutes.
Finally add scallions, stir, turn off heat and serve over white rice.