Slice your sirloin thinly going across the grain of the beef. This ensures the beef stays tender while it's being fried.
Toss the beef with some seasoned cornstarch. Just place the cornstarch in a bowl along with the bicarb of soda and season with salt and pepper.
Once all the strips of sirloin have been tossed in the cornflour, you'll want to get a skillet over high heat. Use a non stick skillet.
Once the skillet is hot, add about a tablespoon of oil and let that warm up. Carefully place the sirloin into the hot pan and leave to brown on one side. This will only take a minute or two. The oil in the pan and the fat from the steak may spit and splash a little, so do be careful.
Once the first side is browned, stir the beef and brown the other sides.
When the beef is brown and crispy, remove it to a bowl or a plate while you mix the sauce. Or you can mix the sauce before getting started.
To Make the Sauce *See notes
To make the sauce simply place all the ingredients in a bowl or measuring jug and stir well.
Once the sauce is mixed, pour it into the hot skillet and bring it up to a boil. It will thicken very quickly, so don't let it bubble for more than about 30 seconds to a minute. Add the beef back into the pan and stir to coat in the sauce.
Serve over noodles or rice and with rocket or broccoli.