In a small bowl, combine the breadcrumbs and milk. Let the mixture stand for 5 minutes until the breadcrumbs have softened and absorbed the milk.
In a large mixing bowl, use your hands to gently combine the ground beef, ground pork, soaked breadcrumbs, Parmesan cheese, beaten egg, parsley, minced garlic, salt, and pepper. Mix just until the ingredients are incorporated; avoid overmixing to prevent tough meatballs.
Lightly moisten your hands with water or oil, then portion the meat mixture into 1 1/2-inch balls, rolling them gently between your palms. You should get approximately 20 to 24 meatballs.
Heat the olive oil in a large skillet over medium heat. Working in batches to avoid crowding, add the meatballs and cook for 8-10 minutes, turning them occasionally, until they are browned on all sides and register an internal temperature of 165°F on an instant-read thermometer.
Transfer the cooked meatballs to a plate lined with paper towels to drain any excess grease before serving, or add them directly to your favorite sauce to simmer.