In a large pot, combine the chicken broth, fresh lemon juice, shredded carrots, finely chopped onion, and finely chopped celery with the chicken soup base and ground white pepper. Bring to a boil over medium-high heat, then reduce heat and let simmer for 15-20 minutes.

While the soup simmers, prepare a thickening paste by mixing margarine and all-purpose flour until smooth. Gradually stir this paste into the simmering soup, cooking for another 8-10 minutes until thickened.

In a separate bowl, beat egg yolks until pale. Temper them by whisking in a ladleful of hot soup, then stir this mixture back into the pot, heating gently.

Stir in cooked white rice and diced chicken until combined. Cook on low heat for about 5 minutes, until heated through.

Ladle the soup into bowls and garnish with fresh lemon slices before serving.