This recipe has many personal touches: The combination of beef and chicken in the base of the recipe is something I got from my mother, studding the chicken with a couple of cloves to add a special flavor from making chicken stock at Guy Savoy in Paris and most of all, the meatballs from my parents. This soup is a meal unto itself and tastes even better leftover.
2 stalks celery with leaves, inner pieces from the bunch peeled of outer skin, cut into 1/2-inch pieces
Soup: Season the chicken with salt, to taste, and push the 2 cloves into 1 of the chicken thighs. Add it to a large stock pot, cover with about 4 quarts water and bring to a simmer over medium heat.
Meanwhile, season the beef bones with salt and brown them in a cast iron pan with the canola oil, searing them over medium heat. Add them to the pot with the chicken. To the pan that the bones were seared in, over medium heat, add the carrots, celery and onion and toss until they are coated in oil. Add the thyme and bay leaves to the stock pot along with the sauteed vegetables. Bring the soup to a gentle simmer and skim the surface with a ladle. Discard any oil or "scum" that accumulates. Sprinkle with a pinch of salt, not too much, and lower the heat to finish cooking the chicken slowly.
Meatballs: Put the ground veal into a medium bowl. Add the salt, garlic, Parmesan, basil, egg and bread crumbs. Use your hands to mix to blend the ingredients. Roll a small meatball and cook a "tester" ladled into the soup, if desired. Taste and reseason the meat mixture, if needed. Roll the rest of the veal into small meatballs. They should be about the size of a small cherry tomato. (Chef's Note: Imperfectly rolled meatballs actually make this soup more homey and real.) Arrange the meatballs in a single layer on a baking sheet and refrigerate.
After about 45 minutes at a gentle simmer, taste the chicken soup and adjust the seasoning, if needed. Use a large spoon and a pair of tongs to remove the chicken to a baking sheet or other flat surface and allow it to cool for a few minutes. Remove the beef bones and scoop out the marrow. Add it to the soup, if desired. Remove and discard the fresh thyme and bay leaves. Take the breast and thigh meat off the chicken, taking care to discard the bones and skin. Break the chicken into bite-size pieces, but not too small, and add them to the soup.
Bring the soup to a gentle simmer and add the meatballs. Allow it to continue simmering for a couple of minutes so the meatballs have a chance to cook. Drizzle in the eggs and continue to mix as they cook. They should look like little threads in the soup. Stir in the spinach and taste for seasoning. Transfer the soup to serving bowls and serve sprinkled with the Parmesan.