In a large pot, combine chicken broth, fresh lemon juice, shredded carrots, finely chopped onion, chopped celery, chicken soup base, and ground white pepper. Bring mixture to a boil, then let it simmer for 15-20 minutes.

In a small bowl, mix the margarine and all-purpose flour together until smooth. Stir this mixture into the simmering soup, allowing it to thicken for 8-10 minutes.

In a separate bowl, beat egg yolks until pale. Slowly pour a ladle of hot soup into yolks while whisking, then stir yolk mixture back into soup pot.

Add the cooked white rice and diced cooked chicken into the soup. Heat on low for about 5 minutes.

Ladle soup into bowls and garnish with lemon slices and optional herbs.