Cut the partridges and braise them in butter until tender.
Remove and set aside the best joints.
Add onions, celery, and 1.7 litres of stock to the remaining bird parts.
Simmer slowly for 1 hour and strain the liquid.
Remove as much fat as possible from the strained stock.
Add bird meat, sugar, and seasoning to the stock and boil briefly.
Skim the surface again to ensure the soup is clear.
Simmer chopped carrot and turnip in the remaining 0.56 litres of stock until tender.
Combine the vegetables and their cooking liquid with the main soup.