If you don't have a deep-fryer (it's not mandatory!) start by pouring your vegetable oil into a medium-sized saucepan until it reaches half way. Don't overfill!
Heat this at a medium heat until it reaches 180-190c or 375f - this takes me around 15 minutes. If you don't have a cooking thermometer to check the heat, then you can test the heat by adding a small cube of gluten free bread. It should brown in 10 seconds at 190c.
While your oil is heating, you can prepare your beef. Before slicing your thinly cut beef steaks, I'd recommend covering them in clingfilm and pounding them with a meat tenderiser or rolling pin to get them as flat as possible. Then, slice them as thinly as you can - the thinner/smaller the strips are, the crispier they'll be.
OPTIONAL: Soak your beef strips in a bowl of water (so the water is just covering the meat) and 1 tsp of salt for anywhere from 1-3 hours. After that time, drain the water away and squeeze as much water out of the meat as possible. This will ensure that the beef is tender and ready for frying.
Combine all of the dry ingredients for your batter and split it 50/50 into two mixing bowls.
Place all of your beef into one of the bowls and mix it around until well-coated and all the flour is used up. Keep squeezing the beef to compact all of the flour onto it.
Pour over your pre-beaten egg over your coated beef. Mix it all around by hand or with a spoon until well-coated.
Lastly, place your coated beef into the second dry batter mix bowl and coat again. Try and separate them as much as poss, though bear in mind that it's not actually possible to keep them all separate! Again, keep squeezing the beef to compact all of the flour onto it.
Carefully lower your twice coated beef into the hot oil - try not to let them clump together too much. Add as much as you can at once so it cools down the oil. It should bubble up nicely. Leave this to fry for about 5 minutes.
Using a slotted spoon or a set of tongs, remove your crispy beef from the oil and place it onto a plate with kitchen roll. This will allow it to drain.
Once you've fried all of your beef, pop it onto an oven tray and place in the oven at 180/200c fan for 10 minutes. This will make it even crispier! At this point (before popping it in the oven) you can always freeze your crispy beef once cooled for another day, and then reheat it by spreading it onto a baking tray and oven-baking it for 20 minutes.
Now for your sauce. Start by pouring in 2 tbsp of garlic-infused oil into a large wok or frying pan and turn on at a medium-high heat. Begin frying your chopped green pepper until softened.
Add in your gf brown sauce and stir thoroughly for around 30 seconds. Then add your gf Worcester sauce and sweet and sour sauce.
Keep stirring and then add your gluten free soy sauce and chilli flakes. Stir in once more and then add your cornflour mixture to thicken the sauce.
Allow the sauce to stay on the heat until it's thickened up a bit and then add all of your now battered and cooked crispy beef strips.
Stir around thoroughly until well coated and nice and sticky. Finish with some sesame seeds and chopped spring onion greens.
Serve immediately and enjoy!