Slice the sirloin steak into thin strips then toss it with the cornflour until the beef is completely coated.
Heat a generous amount of cooking oil in a large frying pan, drop the beef into the oil, cook over a high heat so that it sizzles immediately. You may need to do this in batches so you don't overcrowd the pan.
Cook the beef until it is dark and crispy on both sides. Once crispy, remove from the pan and place the beef onto kitchen paper to soak up any excess oil.
Remove almost all of the oil from the pan, then place the pan back onto a medium heat.
Add the chopped garlic and ginger and cook for a minute. Then add the peppers and cook for a further minute.
Pour in the soy sauce, water, soft brown sugar and black pepper. Mix well.
Turn up the heat and bring it to the boil, then turn it down to a simmer. Cook for 2-3 minutes.
Add the beef back into the pan, cook for a further 2-3 minutes. The sauce should become thicker and stick to the beef.
Turn off the heat and stir through the sliced spring onions.
Serve immediately with rice or noodles.
