Combine all the ingredients except milk or cream in a large saucepan and bring to boil, over moderate heat, stirring from time to time.
Reduce heat and simmer gently and partly covered for 20 minutes.
Mix the milk or cream with the cake flour and stir into the soup.
Simmer and stir to thicken. Adjust seasoning and consistency by adding a little extra milk or water if the soup is too thick.
Serve piping hot.