Melt 8 oz (2 sticks) butter in a heavy saucepan. Add the flour and cook over, over medium heat until the roux is light brown, stirring frequently. Set aside. If turtle bones are available, add them to the beef bones when making the stock for this dish.
In a 5-qt saucepan, melt the remaining butter and add turtle meat. Cook over high heat until the meat is brown. Add celery, onions, garlic and seasonings, and cook until the vegetables are transparent.
Add tomato purée, lower heat and simmer for 10 minutes. Add the stock and simmer for 30 minutes. Add the roux and cook over low heat, stirring, until the soup is smooth and thickened. Correct seasoning with salt and pepper to taste. Add lemon juice, eggs and parsley.
At the table, add 1 tsp sherry to each soup bowl.