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 20-30 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 jar and shake briefly. Set aside. Dissolve cornflour in water and set aside too.
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).
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.
Deep fry the pork in two batches for 3 minutes. Use a 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).
Move pan with hot oil out of the way and place a wok on the hot burner.
Heat 1 tbsp oil in the wok and stir fry the peppers with 1 tbsp water 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 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!