Cut the beef into really thin strips, coat in baking soda and leave for 30 minutes.
Rinse the beef well in a colander to get rid of the baking soda and put in a bowl. Add soya sauce, garlic and ginger and let marinate for at least 20 minutes (over night in the fridge is the best!).
Mix all the ingredients for the sauce and set aside while cooking the beef.
Coat the meat in 3 tbsp of corn starch and leave for 10 minutes. Add the last 1 tbsp and then start frying the meat!
Make sure the oil is hot when you put the meat in, and cook it in batches. Because the meat is so thinly cut, it only takes 1-2 minutes to cook it. Scoop up from the pan and let dry on some kitchen towels.
When the beef is done, pour most of the oil out of the pan, turn the heat down and cook the onions for a couple of minutes. Pour the sauce over the onions and let simmer for a minute.
Add the beef to the sauce and plate up!
