Mix the cornflour with 1/4 cup water and keep aside. In a deep bowl, combine chicken stock and sweet corn. Bring it to a boil. Reduce the flame to low and add cornflour. Mix well. Cook for 2-3 mins. Drizzle the beaten egg through a strainer. Cook for 2-3 mins. Add cooked chicken, soya and vinegar if using. Cook for 2-3 mins. Add pepper powder, salt and sugar. Mix well and remove from fire.
For chicken stock
Combine all the ingredients except water in a deep pan and mix well. Add water and bring it to a boil. Remove the white foam formed on the top. Reduce to low flame and let it cook for 20-25 mins.
If you want to store the stock for later use, let it cool down completely. Pour it on ice tray and freeze it. Once it is set, store the stock cubes in ziplock bags in freezer.