In a large soup pot, combine the broth, lemon juice, onion, carrot, celery, and boullion. Simmer for 20 minutes.
Then gradually whisk in the ghee and flour. Simmer for 10 minutes, stirring frequently.
Meanwhile, whisk the egg yolks until they lighten in color, about 2 minutes.
Gradually add about 1 cup of the hot soup to the egg yolks, a little at a time, to bring the eggs up to temperature without turning them into scrambled eggs.
Add the egg mixture to the soup pot and heat through.
Add the rice, chicken, and ground white peppercorns.
Ladle hot soup into bowls and garnish with lemon slices.