Make the soup: In a large pot or Dutch oven, heat the olive oil over medium heat. When the oil is hot add the meatballs, turning occasionally, just tow warm through. Transfer to a paper towel-lined plate.
Step 3
Add the onion, carrots and celery to the pot and cook, stirring occasionally, until the vegetables are crisp-tender, about 10 minutes. Add the garlic, 1 teaspoon of salt (or 2 teaspoons if you’re using low-sodium broth) and ½ teaspoon black pepper. Cook until the garlic is fragrant, about 1 minute.
Step 4
Return the meatballs to the pot, add the broth and bring to a simmer over medium-high heat. Stir in the pasta, lower the heat and simmer, stirring occasionally, until the pasta is tender, about 10 minutes.
Step 5
Turn off the heat and stir in the spinach until wilted. Taste and season with salt and pepper, if needed. (The broth should taste pleasantly salty.) Serve hot, topped with Parmesan. The pasta will continue to absorb liquid as the soup sits; you may need to add broth when reheating. Soup will keep for up to 5 days in the refrigerator or 3 months in the freezer (see Tip).
Tip
To freeze, cool soup to room temperature in the pot, then transfer to airtight containers and freeze for up to 3 months. Thaw overnight in the fridge, or run the container under hot tap water until the soup releases. Transfer to a pot and bring to a simmer, partially covered, adding more water or broth if necessary.