1. Cut 3 of the carrots crosswise into quarters. Cut 4 of the celery ribs crosswise into quarters. Cut onions into 8 equal wedges.
2. Place carrot pieces, celery pieces, onion, parsley, garlic, thyme, peppercorns, and bay leaf into 6- to 8-quart pot; add chicken. Add enough cold water to cover. Bring to boiling over high heat. Boil 3 to 5 minutes, skimming off foam from surface as it appears. Reduce heat; simmer, uncovered, for 3 hours, skimming the fat as needed. Add water if necessary in order to keep the chicken covered.
3. Pour the soup into a colander over a bowl large enough to hold liquid; discard the vegetables and bay leaf. Let the chicken stand until cool enough to handle.
4. Dice the remaining carrot and the 2 celery ribs.
5. Return chicken broth to pot. Add the salt. Bring to boiling.
6. Meanwhile, remove skin from chicken. Remove chicken from bones and tear into shreds.
7. Add diced carrot, diced celery, tomato and orzo to boiling broth. Skim any fat. Boil 5 minutes. Add reserved chicken shreds. Cook for 5 more minutes or until orzo and vegetables are tender. Makes 8 servings.