Naturally, the key to making turtle soup is ground turtle meat, which is available in many meat markets and especially in small, ethnic groceries. Ground veal works well as a substitute, but you can't call it turtle soup when there's no turtle in the pot.
To cook the turtle meat, bring 4 quarts of water to a boil in a large pot and simmer the meat for 45 minutes. Drain off the water and coarsely chop the meat. Set aside until needed.
In a large pot, bring the chicken stock, garlic, bay leaves and thyme to a boil. Add the tomato paste, vegetables, parsley and lemons. When boiling again, reduce the heat and simmer for 10 minutes. Add the meat and the sherry, return to a boil, then reduce heat and simmer for 5 minutes. Add the eggs. Season to taste with salt and pepper. Thicken if desired by adding small amounts of roux. Serve in soup bowls, preferably with a final splash of sherry.