By An Edible Mosaic
Heat the oil in a 5-quart Dutch oven over high heat. Once hot, add the chicken, skin-side-down. Sprinkle on the salt and black pepper. Sear until the chicken skin is golden brown.
Add the onion, 5 cups chicken stock, and bay leaf, and bring it up to a boil. Cover the pot and cook until the chicken is fully cooked, about 20 minutes, turning the heat down as necessary.
Once the chicken is fully cooked, use tongs to remove it. Let it cool, then pull the chicken off the bone and chop it up (discard the skin and bones).
Stir the remaining 5 cups chicken stock, chopped chicken, carrot, celery, garlic, and thyme into the soup. Bring back up to a boil, and then boil 5 minutes.
Use a 1-tablespoon scoop to measure the chilled matzo ball mixture. Once the mixture is measured out, roll into balls between the palms of your hands (it helps to wet your hands).
Drop the matzo balls into the boiling water. Cover the pot and cook for 20 minutes, turning the heat down as necessary. Add the parsley and serve.