In a large bowl, combine ground beef, bread crumbs, Parmesan cheese, parsley, garlic, egg, milk, salt, and pepper. Mix everything thoroughly until well combined.
Shape the mixture into meatballs, about 1-1/2 inches in diameter. Ensure they are compact so they won’t fall apart during cooking.
Heat olive oil in a large skillet over medium heat. Once the oil is hot, carefully add the meatballs in batches, avoiding overcrowding the pan.
Brown the meatballs on all sides, turning occasionally, for about 5-7 minutes until fully cooked. Ensure they are golden brown outside and fully cooked inside.
Once the meatballs are browned, pour marinara sauce over them. Stir gently to coat each meatball with sauce, then reduce heat to a simmer.
Cover the pan and let the meatballs simmer in the sauce for 15-20 minutes to absorb the flavors. Serve hot with extra Parmesan cheese.
