Place the bones in a large saucepan, braise until lightly browned and cover with fresh cold water. Bring to boil.
Remove any froth that forms on top, then simmer, covered, for 3 hours or until meat is failing off bone, topping up with water as needed. At end of cooking time you should have about 1,5 litres (6 cups) stock - top up with water if necessary to make up quantity.
Wash and finely chop parsley and celery. Peel onion, make small incisions and insert bay leaf and cloves in slits. Add to stock with thyme, salt and whole peppercorns. Simmer for 1 hour.
Sieve stock and allow to cool. (At this point you can cool stock, pour into containers and freeze until needed, if you need a larger quantity, double the recipe.)
Refrigerate overnight, covered. The next day, remove any fat on surface.
To clear stock, add egg whites and shells and, whisking constantly, bring to boiling point over low heat, then simmer for 20 minutes. Cool slightly.
Sieve stock again, through a colander lined with muslin.
Clean carrot, leek and celery and cut into thin julienne strips. Blanch in salted, boiling water then pour iced water over. Drain and add to hot stock.
Add Madeira or sherry to taste. Chill, then divide between soup plates or bowls. Just before serving, add edible blossoms.
TOTAL KILOJOULE COUNT: 1 260 kJ (300 Cal). A portion: 210 kJ (50 Cal)