Cut undercut into ½ inch thick pieces of meat, apply salt and keep aside.
Heat oil in a wok, coat meat pieces first with egg and then corn flour, fry till golden.
Heat 2 tbsp oil in a wok, fry garlic and onion, spring onions, capsicums and pineapple pieces.
Mix sugar, tomato ketchup, chicken stock, soy sauce, corn flour and salt in vinegar, put in wok.
Cook for 5 minutes.
Add the beef and mix.
Pour the dish in a serving bowl.
Serve hot.
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