Thinly slice the beef against the grain and put it in a small bowl.
Add in all the ingredients from 'Beef Marinade' and mix it into the beef by hand.
Velveting
Traditional Method : In a large wok or pot, add enough oil (or water) to be able to fully submerge the beef.When the oil is hot, add the beef into the oil and use a metal spatula to move it around to separate the beef slices.Cook it until the beef is only 50% cooked, about 30 seconds.Remove the beef from the wok and set it aside to use for a stir fry.
Easy Method : In a large wok, add about 2-3 tablespoons of oil.When the oil is hot, add in the beef and use a spatula to separate the beef slices into a thin layer and let it cook for about 15 seconds.Use the metal spatula to flip all the beef to the other side to cook for another 15 seconds. You don't want to fully cook the beef.Remove the beef from the wok and set it aside for when you're ready to use it for a stir-fry.
Notes
Adding water to any type of chicken, pork, or beef marinade not only rehydrates the meat so that it becomes juicier and moister but when combined with soy sauce it also makes it a mini brine which gives it another level of hydration so your beef always stays tender and juicy.
Alternatively, if you don't want to use corn starch for velveting beef, you can also use tapioca starch or potato starch but any type of starch will actually do the trick.
For the neutral oil, I like to use avocado oil but any type of oil will work as well.