Mix the cornflour and water. Keep aside.Peel and chop the potatoes into long thick chunks.Heat oil in a wok or pan, add some potatoes at a time.Fry till light golden brown. Finish all potatoes similarly.Keep aside. Remove half the oil.In the remaining oil, add the chillies, ginger and garlic.Fry for a minute. Add the potatoes.Add sauces, salt and sugar. Stir well and add the cornflour solution. Cook till the wateriness is gone.Add spring onions and stir. Serve hot.