Step 1

In a large Dutch oven or heavy-bottomed pot over medium-high, add the olive oil and sausage and saute, stirring every so often, until browned on all sides, about 5 minutes. Increase the heat to high and add the carrots, celery and broth. Cover, bring to a boil and cook until the carrots and celery are tender, 10 to 12 minutes. Remove from heat.

Step 2

Meanwhile, make the meatballs: Position a rack in the middle of the oven and preheat it to 425 degrees.

Step 3

In a large bowl, add the milk or water and egg and whisk lightly. Add the slice of bread and soak for 5 minutes. Add the ground pork or turkey, cheese, onion, parsley, garlic, salt and pepper to the soaked bread and mix with your hands until combined. Rinse and moisten your hands with cool water and then shape the mixture into 1- to 2-inch meatballs; you will have 30 to 35 meatballs. Place them, spaced evenly, on a sheet pan. Bake for 10 to 12 minutes; meatballs will finish cooking in the soup.

Step 4

Return the heat to high under the soup. As soon as the broth comes to a boil, stir in the pasta and simmer until al dente, 4 to 6 minutes. Lower the heat to medium, and stir in the chopped greens, red pepper flakes, if using, and half of the lemon zest.

Step 5

Using a spatula, scrape the meatballs and any fat and crispy bits stuck to the pan into the soup. Increase the heat to high and cook until the greens soften and the meatballs are cooked through — cut into one to be sure it’s no longer pink in the center — about 3 minutes.

Step 6

Add half of the lemon juice; taste the broth, and season with additional salt and pepper, if desired.

Step 7

Serve the soup hot, garnished with celery leaves, Parmesan, parsley, dill, the remaining lemon zest and juice, if desired.