In a large pot, combine the chicken stock, lemon juice, carrots, onions, celery, soup base, and white pepper. Bring to a boil on high, then simmer for 20 minutes.
Blend the butter and the flour together. Then gradually add it to the soup mixture. Simmer for 10 minutes more, stirring frequently.
Meanwhile, beat the egg yolks until light in color. Gradually add some of the hot soup to the egg yolks, stirring constantly. Return the egg mixture to the soup pot and heat through. Add the rice and chicken. Ladle hot soup into bowls and garnish with lemon slices.