Bring the chicken breast to the boil in 1 1/4 litre of water and simmer for about 45 minutes. Skim from time to time. In the meantime, peel the onion, halve it and fry it in a hot pan.
Add the onion to the stock. Clean and peel the carrots and celery and add them to the stock. Remove the chicken breast and remove the fillets from the bone. Peel skin and add parsley and bay leaf together with the bone back to the broth.
Let simmer for another 15 minutes. Meanwhile clean the broccoli, divide into small florets and blanch in boiling salted water for about 5 minutes. Remove and rinse with cold water. Drain. Wash, clean and quarter the tomato.
Remove cores. Cut the tomato quarters into cubes. Cut chicken fillets into pieces. Put chicken soup through a fine sieve into a pot. Bring to the boil. Heat chicken breast, broccoli and tomato in it.
Season with salt. Arrange in soup plates.