Tuscan Onion Soup(Carabaccia)

"The Tuscans will tell you they invented onion soup—one of the best-known versions of this soup, carabaccia, was jotted down in a 1500s cookbook. Serve it with or without the eggs, but I think they add great sustenance to this otherwise very simple soup. If you want richer flavor, you can use chicken stock, or fry some pancetta or sausage pieces and add them to the soup. In the springtime, a version of this soup includes fresh peas (frozen will do) and fava (broad) beans. You can make the soup ahead with everything except the eggs and Parmesan and simply add these once you have reheated the soup. This is edited slightly from my cookbook "Florentine: The True Cuisine of Florence," published by Hardie Grant Books, 2016 (in the original I call for making your own vegetable stock, but for ease, I didn't specify—but obviously, for such a simple recipe, use a good quality one, whichever way you decide to go). Featured In: You Know French Onion Soup—But Do You Know Its Tuscan Mother?..."