In a large bowl, mix all of the ingredients for the meatballs together except for the olive oil. I find this is easiest to do with my hands by squishing until everything is evenly combined. Just try not to overwork the meatballs or they will be tough.
Shape the meat mixture into small 1-inch meatballs. I usually end up with about 50-60 meatballs, depending on how small I make them.
Heat 2 tablespoons of the olive oil in a large pot or dutch oven over medium-high heat. Add the meatballs in a single layer and brown for 2-3 minutes on each side (the meatballs don't need to be cooked all the way through, just browned to give them color and flavor). You may need to work in batches to brown all of the meatballs. Transfer the browned meatballs to a plate. Drain any grease.
Using the same pot or dutch oven, add the remaining 1 tablespoon of olive oil. When it is hot, add the carrots, onion, and celery. Saute for 4-5 minutes until the vegetables begin to soften.
Add the chicken and beef broths, along with the basil, oregano, rosemary, thyme, salt, and pepper. Bring to a boil, then reduce the heat to medium and add the meatballs and acini de pepe pasta. If using a tougher green like kale, chard, or curly endive, add it at this point as well.
Simmer for 10-15 minutes, stirring occasionally, until the meatballs are cooked through and the pasta is al dente. Stir in the spinach (if using), then serve. Garnish with the freshly parsley and Parmesan cheese.