4boneless skinless chicken breastsdiced (about 2 pounds; see Note)
2 ½cupscooked orzo
½cupfresh lemon juice
¼cupminced fresh dill or parsley(optional)
In a large soup pot or Dutch oven, heat the olive oil over medium heat. Add the onion and sauté for about 5 minutes until slightly golden. Add the broth, and turn the heat to high. Bring the broth to a simmer.
Lower the heat to medium, and keeping the broth at a simmer, add the diced chicken breasts. Cook for 5 minutes until the chicken is mostly cooked through. Add the cooked orzo.
In a medium bowl, beat the eggs, and then beat in the lemon juice. Working quickly, whisk the egg mixture while you drizzle in a ladleful of the hot broth from the pot (see Cooking Tip). Drizzle in another ladleful, whisking all the while, then transfer the hot egg-lemon mixture back to the pot, whisking as you add it. Bring to a simmer over medium heat.
Simmer for a couple of a minutes, stir in the dill or parsley if using. Serve the avgolemono soup hot.
Cooking Tip: Egg in the Broth
What you are doing here is tempering the egg mixture. If you were to add the egg mixture to the pot all at once, even if you whisked very fast, you would still end up with cooked strands of eggs punctuating the soup (in some soups, this is desirable – think about egg drop soup at a Chinese restaurant). Add the hot liquid in slow steady amount to the eggs, while whisking all the while, thickens the eggs but the whisking keeps them from cooking in a clump, and then once that mixture has become thick and smooth, and warm, you can whisk it back into the soup and it will simply thicken the whole pot of avgolemono.