Mix the soy sauce with the vinegar, sugar and stock. Stir the cornflour into 2 tbsps water until dissolved, then add to the stock mixing well.
Cut the pork into thin slices then toss in cornflour mixed with a generous pinch of salt.
Heat the oil in a wok and when hot add the pork. Stir and fry until the edges have caramalised, keeping the heat high. Scoop out the pork with a slotted spoon and set aside.
Add the mushrooms and fry for 1-2 minutes until golden, then remove with a slotted spoon and add to the pork.
Add the shallots, ginger, chillies and garlic to the remaining oil in the pan and stir fry until the garlic is a deep gold and soft then add the pork, mushrooms and stock to the pan, stirring as the mixture thickens.
Add a few shakes of soy then the coriander leaves. Serve with rice or mashed potato.