Place 3 quarts water into large saucepan and bring to a boil over high heat. Add chicken breasts and onion to water and turn heat to medium high. Skim foam off water as forms. Cook until chicken is tender and cooked through. Remove chicken to plate to cool.
Place celery stalks, carrots, parsley, pepper and chicken soup base into water and taste for flavor. Adjust seasonings. Let simmer until chicken has cooled and has been cut into bite-sized pieces.
Remove celery stalks and return chicken to soup. Simmer about 15 minutes. Add cooked noodles, cook another 10 minutes to heat through and serve immediately. Makes about 8 to 10 servings. Enjoy!