In a bowl large enough to fit the beef, mix one teaspoon oil, one teaspoon soy sauce and one tablespoon cornstarch into a paste. Slice the beef in 1/4" slices, against the grain. Toss well in the soy and cornstarch mixture, and let sit for 30 minutes at room temperature.
In a shallow skillet, heat the remaining fry oil on high heat so that it is really hot. While you are waiting for it to heat, coat the beef in the remaining corn starch.
Carefully lower one piece of beef into the oil to see if it is hot. If hot enough to fry the beef, place the rest of it in the pan and cook for about a minute or two, turning once. If the oil is not hot enough, the beef will just absorb the oil and the cornstarch will become wet and un-crunchy.
Once ready, take the beef out of the pan and allow it to drain, either placing on a plate with paper towels or a plate tilted a bit on an angle so the excess grease separates.
Discard all of the oil except for about a tablespoon. Add the garlic, ginger, chili, remaining soy sauce and scallions (if you are using chives, don't include them) and stir well until garlic is nicely browned.
Next add the vinegar and sugar and cook, stirring well until the vinegar is reduced and sugar dissolved. Lower the head a bit to do this.
Return the beef to the pan and cook for another 30 seconds until everything is coated nicely.
Top with the chives if you use them and serve with rice or noodles.