3 Tbs. plain fresh breadcrumbs
1/4 cup finely grated Parmigiano-Reggiano; more for serving
2 Tbs. chopped fresh flat-leaf parsley
Kosher salt and freshly ground black pepper
1/2 lb. ground chicken
1 large egg
1 Tbs. extra-virgin olive oil
1 small yellow onion, cut into small dice
1 small carrot, cut into small dice
1 medium celery stalk, cut into small dice
1 quart lower-salt chicken broth
1 3- to 4-inch sprig fresh rosemary
5 cups thinly sliced escarole
Put the breadcrumbs in a medium bowl and moisten with 1/2 Tbs. water. Mix in the Parmigiano, parsley, 3/4 tsp. salt, and 1/2 tsp. pepper. Add the ground chicken and egg and mix until just combined. Scoop out 1 Tbs. of the chicken mixture and, with damp hands, roll it into a 3/4-inch meatball. Transfer to a plate and shape the remaining meatballs.
Heat the oil in a 5-quart pot over medium heat. Add the onion, carrot, celery, and 1 tsp. salt; cook until tender, 3 to 4 minutes. Add the chicken broth, rosemary, and 2 cups of water; bring to a boil over medium-high heat. Gently add the meatballs, reduce the heat to medium low to maintain a gentle simmer, and cook for 10 minutes.
Add the escarole and continue to simmer until the meatballs are cooked through and the escarole is wilted, about 5 minutes. Discard the rosemary and season to taste with salt and pepper. Serve sprinkled with grated Parmigiano.
