Italian wedding soup

The first time that I had this soup was when I was a college student in New York. I think I had gotten a small cup of takeout soup from Dean and Deluca and brought it back to my dorm room. Instantly, I fell in love with the soup, not just the romantic name, but also the warm comforting broth and hearty vegetables. Here, quantities are approximate and feel free to vary the soup based on what you have on hand.

2-3 cups mini meatballs ( I make them ahead and throw them in frozen, thus the soup is almost effortless, use any meatball rec., fully cooked)

2-3 Tablespoons olive oil
2 medium yellow onions, peeled and fine dice
2-3 small carrots, peeled and roughly chopped
2-3 stalks celery, roughly chopped
3 Quarts chicken stock
1-2 heads of escarole (about 1 1/2-2 pounds) tough stems removed and roughly chopped
3/4 cup pastina pasta (optional)
salt and ground pepper for seasoning
grated parmesan cheese for serving

Start by warming you oil over medium heat in a 5 quart Dutch oven or pot, once warm add the onions, carrots and celery and reduce heat to medium low. Cook for 7 minutes, stirring often. Add the chicken stock. Then, bring to a boil, add the frozen mini meatballs and escarole. Simmer 10 minutes. Add in the pastina and cook another 6 minutes. Season with salt and pepper as needed. serve with grated cheese.