Pour the chicken broth into a large saucepan, and bring it to the boil. Add the pasta and cook for 5 minutes.
Beat the eggs until frothy, then add the lemon juice and 1 tablespoons of cold water. Slowly stir in a ladleful of the hot chicken stock, then add one or two more. Be careful not to scramble the eggs!
Return this mixture to the pan, off the heat, and stir well. Season with salt and pepper and serve at once, garnished with lemon slices. Do not let the soup boil once the eggs have been added or it will curdle!