Some people put carrots in their escarole soup. Some put celery. Some rice. They're probably all fine and good recipes. I wouldn't know, I've been trying to replicate Mom's for about 10 years and hers doesn't have any of that fancy stuff — doesn't need it.
Its main components are escarole, onion, garlic, chicken stock, and cannellini beans. That makes it a very easy soup to make. It's kind of the ideal soup because it's heartwarming but thin — so it works year-round. It will fill you up, but you don't feel heavy after eating it — just satisfied. The beans kind of leak out their starchiness, thickening it a little once the soup has had a chance to sit.
A tablespoon of red pepper flakes while it's cooking gives it a little edge, and sprinkle of Parmesan to finish once you've ladled it out is the perfect finish. It's almost always better the second day.
For the soup:
This might be the most simple recipe I have. It's easy. Watch this. Warm the olive oil in a large pot over medium heat and then sauté the garlic and onion. Add the stock to the pot. A couple of minutes later, throw the escarole and beans in the pot. Add the red pepper flakes, lemon juice, salt, pepper, and bay leaf. Simmer for an hour, remove the bay leaf, and eat with a sprinkle of grated Parmesan. Even better the next day.