In a large pot, combine 8 cups of chicken broth, 1/2 cup of fresh lemon juice, 2 shredded carrots, 1 chopped onion, 2 chopped celery stalks, 2 tablespoons chicken soup base, and 1 teaspoon ground white pepper. Bring to a boil, then simmer for 15-20 minutes until the vegetables are tender.

In a small bowl, mix together 2 tablespoons of margarine and 1/4 cup of all-purpose flour to create a smooth paste. Gradually stir into the simmering soup for about 8-10 minutes.

In a separate bowl, beat 3 egg yolks until pale. Slowly add a ladleful of hot soup while whisking to prevent curdling. Pour back into the pot, stirring gently, and heat for another 3-5 minutes without boiling.

Stir in 1 cup of cooked white rice and 2 cups of diced cooked chicken, warming through for about 3 minutes until heated evenly.

Ladle the soup into bowls and garnish each serving with a lemon slice. Serve warm, optionally with crusty bread.