Prepare the Meat Mixture: In a large bowl, combine ground beef, ground pork, breadcrumbs, Parmesan, garlic, parsley, milk, egg, salt, pepper, and Italian seasoning. Mix gently until just combined—do not overmix.
Shape the Meatballs: Form the mixture into golf-ball-sized meatballs (about 12-14 pieces).
Sear the Meatballs: Warm olive oil in a large pan over medium heat. Brown the meatballs on all sides, about 5–7 minutes total. They don’t need to be fully cooked at this stage.
Simmer in Sauce: Pour marinara sauce into the skillet with the meatballs. Cover and simmer on low heat for 20–25 minutes, or until meatballs are cooked through.
Serve: Serve hot over spaghetti or with garlic bread. Top with additional Parmesan and chopped parsley if you like.