Rinse the chicken, place in a suitable pot, cover with about 1.5 liters (approximately 6 cups) of water, the onion, bay leaf, and peppercorns. Bring to a boil, cover, and simmer about 1 hour. Meanwhile, peel the carrots and rinse the remaining vegetables. Cut the carrots and celery into sticks. Chop leeks and parsley. Take chicken out of pot and remove the skin and bones and cut into bite-size pieces, pour the soup through a sieve, and return it to the pot with the chicken meat and all the prepared vegetables. Simmer for another 20 minutes.
Season with salt and pepper and simmer for 5 minutes. Add parsley. Serve garnished with herbs and croutons or breadsticks.