Heat the oil in a wok or large frying pan until very hot.
Mix the cornflour with a good pinch of salt and pepper and toss the steak strips in the cornflour.
Cook the steak strips in the oil (turning occasionally) until very dark and crispy. You can do this in two batches, but I usually manage this in one. You just need to make sure the oil is really hot, and then leave the steak cooking in the oil for a good 5 minutes before turning. Don't keep moving it around the pan, or you won't achieve that dark, crunchy coating.
Use a slotted spoon to remove the beef from the pan. Place it on a plate with some kitchen roll on to drain off excess fat.
Pour out all but 1 tbsp of oil from the pan, turn the heat down to medium and allow the oil to cool a little. Add the ginger and garlic to the pan and cook for 1 minute - stirring often to avoid burning the garlic.
Add in the soy sauce, pepper, sugar and water into the wok.
Give it a good mix and turn up the heat and bring to the boil. Simmer for 2-3 minutes.
Then add the crispy beef back to the wok and cook for a further 2 minutes.
Then turn off the heat and stir in the spring onions (scallions).
Serve over boiled rice.
Can I make it ahead? This stir fry tastes best when made right before serving as that's when the beef will be most tender. However, you can quickly cool, cover and refrigerate leftovers for up to a day in the refrigerator. Reheat in the microwave until piping hot.Do I have to eat it with rice? Mongolian beef goes well with rice, but you can also eat it with noodles, cauliflower rice or stir-fried veg.I can't find muscovado sugar. Can I use something else instead? Muscovado sugar has a beautiful roasted flavour. So it's preferable that you use it. But if you absolutely cannot find it, any light or dark brown sugar will work.Nutritional Information is per serving, without the serving suggestion of boiled rice.