gluten freePrep the vegetables
Peel the onion and cut it in half through the root so it stays together in the pot. Peel the carrots, if you like, and cut them into large chunks. Trim the ends from the celery and cut the stalks into similarly large pieces so they can flavor the broth without falling apart.
Simmer the chicken
Place the whole chicken in a large heavy pot. Check the cavity and remove any giblets if they are inside. Pour in enough water to cover the chicken by about 1 inch, then add the onion, carrots, celery, bay leaves, black peppercorns, olive oil, and fine sea salt. Bring everything just to a boil over medium-high heat, skim off any foam that rises to the top, then lower the heat so the liquid stays at a very gentle simmer. Partly cover and cook for 1 hour 15 minutes to 1 hour 30 minutes, until the chicken is very tender and the legs move easily when nudged.
Strain and cool
Lift the chicken out onto a tray or large plate. Pour the broth through a fine-mesh strainer into a clean pot or large bowl, pressing lightly on the vegetables to catch their liquid, then discard the cooked vegetables, bay leaves, and peppercorns. Let the chicken rest for 10 to 15 minutes, until it is cool enough to handle comfortably.
Shred the chicken
Pull the meat from the bones in bite-size pieces, discarding the skin and bones as you go. Keep the shredded chicken covered so it does not dry out, and pour any juices collected on the tray back into the strained broth for extra flavor.
Rinse the rice
Put the white rice in a sieve and rinse it under cold running water, swishing the grains with your fingers, until the water runs mostly clear. This helps the soup stay light and brothy instead of becoming overly starchy.
Cook the rice
Bring the strained broth back to a gentle boil. Stir in the rinsed rice, lower the heat, and simmer for 15 minutes, stirring once or twice, until the rice is tender but still holding its shape.
Whisk the avgolemono
While the rice cooks, crack the eggs into a medium bowl and whisk them until smooth and a little frothy. Cut and squeeze the lemons to make 1/2 cup juice, removing any seeds, then whisk the juice into the eggs. Slowly whisk in 1 ladleful of hot broth, then a second ladleful, so the mixture warms up gradually and becomes smooth and satiny.
Finish the soup
Reduce the soup to low heat or take the pot off the heat for a moment. Stir the shredded chicken back into the broth, then slowly pour in the tempered egg-lemon mixture while stirring constantly. Warm the soup gently for 2 to 3 minutes, just until it looks lightly creamy and silky; do not let it boil or the eggs can curdle. Taste and add more salt if needed.
Serve hot
Ladle the kotosoupa into bowls and serve it right away while it is hot and fragrant. The broth should be glossy, the rice tender, and the finish bright and velvety from the avgolemono.
