In a food processor, process the onions, parsley, and garlic until finely chopped.
Transfer the onion mixture to a large bowl and add the turkey, Parmesan, eggs, bread crumbs, milk, 1 teaspoon salt, and 1/2 teaspoon pepper. Use your hands to gently combine.
Form the meat mixture into 48 meatballs (about 2 tablespoons each). The meatballs can be frozen at this point.
Heat broiler. Place the meatballs on a foil-lined broilerproof rimmed baking sheet and broil, turning once, until cooked through, 8 to 12 minutes.