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

In a small bowl, blend margarine with all-purpose flour until smooth. Gradually stir this into the simmering soup, cooking while stirring for 8-10 minutes until thickened and creamy.

In a separate bowl, beat egg yolks until creamy. Slowly incorporate a ladleful of hot soup while whisking. Then pour back into the pot while stirring, gently heat for 2-3 minutes without boiling.

Add cooked white rice and diced cooked chicken to the pot, stirring to combine. Heat over low for 3-5 minutes until warmed through.

Ladle the soup into warm bowls, garnishing with a slice of lemon to enhance flavor.