Adding egg to thicken a soup is a little tricky as it will curdle or scramble if overheated. Beat one or two egg yolks (or whole eggs) in a bowl and stir in a little of the hot soup. Then strain this into the pan and stir over a gentle heat until thickened; do not allow it to boil. This method can be used for a hot soup or one to be served cold (which will thicken further on cooling). For a richer soup, the eggs can be mixed with cream.
** Asian Recipes