Prepare pork marinade by combining the soy sauce, egg yolk and 1 tbsp of cornstarch together in a medium sized bowl. Stir in the pork pieces and leave to marinade for 30 minutes.
Meanwhile, prepare peppers, onion, garlic and pineapple and place in separate bowls. It can get frantic while cooking and so having everything prepared in advance makes it much easier.
Prepare sauce by combining the pineapple juice, vinegar, sugar, water and tomato sauce together in a small bowl. Set aside.
Stir the remaining 6 tbsp cornstarch into the pork. It gets a bit gloopy but I find once it's well combined you can separate the pork pieces onto two plates for ease of handling. They'll separate during frying.
Heat the oil in a large heavy bottomed pan to 180 °C. Keep the lid nearby just in case the oil gets too hot and catches fire (just pop the lid on to put it out).
Deep fry the pork in two batches for 3 minutes. Use a kitchen timer! Remove pork with a slotted spoon and place on a plate next to the cooker.
When both batches of pork have been cooked pop them all back into the hot oil for a further 30 seconds. Remove with a slotted spoon and drain in a bowl lined with kitchen towel. Keep warm (I put a plate over the top to keep the heat in).
Heat 1 tbsp oil in a wok or frying pan and stir fry the peppers for 2 minutes. Remove peppers and keep warm.
Add remaining 3 tbsp oil and stir fry the garlic for 30 seconds. Add the onion and pineapple and stir fry for a further minute.
Return peppers to the pan and pour in the sauce.
Bring to the boil and stir in the cornflour dissolved in the water to thicken.
When thickened stir in the pork pieces and toss lightly to coat the pork in the sauce completely.
Serve immediately with rice or noodles.
A typical 435 gram tin of sliced pineapple in the juice will give you enough pineapple to make this recipe, plus 4 slices leftover for a pineapple upside-down cake for afters if you fancy!