Preheat your oven to 400°F. Line a large rimmed baking sheet with parchment paper and set aside.

In a large bowl, combine the ground beef, ground pork, breadcrumbs, Parmesan, egg, garlic, parsley, salt, pepper, and oregano. Mix gently with your hands until just combined — do not overwork the mixture or the meatballs will be tough.

Using a teaspoon or a small cookie scoop, roll the meat mixture into small balls about 3/4 inch in diameter (roughly the size of a large marble). You should get approximately 40-48 mini meatballs. Place them on the prepared baking sheet in a single layer.

Bake for 15-18 minutes, until lightly golden and cooked through. Set aside.

While the meatballs bake, heat olive oil in a large Dutch oven or heavy-bottomed pot over medium heat. Add the diced onion, carrots, and celery. Cook, stirring occasionally, for 6-8 minutes until softened and the onion is translucent.

Add the minced garlic and cook for 1 minute more, stirring frequently, until fragrant.

Pour in the chicken broth. If using a Parmesan rind, add it now. Increase heat to medium-high and bring to a gentle boil. Season with salt and pepper.

Once the broth is boiling, add the acini de pepe pasta. Cook for 8-10 minutes, stirring occasionally, until the pasta is just al dente.

Add the baked mini meatballs to the pot and stir gently to combine. Simmer for 2-3 minutes to warm the meatballs through and allow the flavors to meld.

Remove and discard the Parmesan rind if used. Add the fresh baby spinach and stir until it wilts into the broth, about 1-2 minutes.

Taste and adjust seasoning with additional salt and pepper as needed. Ladle into bowls and serve immediately, topped with a generous shower of freshly grated Parmesan cheese.