Add the onion to the saucepan and cook for 3 to 4 minutes. Add the chicken stock and potatoes, cover and simmer for 15 minutes.
Mix the cornflour with a small amount of the milk, then stir in the remaining milk. Add this liquid to the soup mixture with the sweet corn and chicken. Reheat, stirring constantly, until the soup thickens. Season to taste and stir in the parsley. Add a little more milk if too thick for your liking.
Serve the chicken & sweet corn chowder with a sprinkle of fresh parsley and slices of fresh bread.