Combine ground beef, ground pork, minced onion, bread crumbs, parsley, salt, pepper, Worcestershire sauce, egg, and milk in a large bowl.

Mix all ingredients thoroughly until well combined, but do not overmix.

Shape the mixture into small balls, approximately the size of a walnut.

Heat fat or vegetable oil in a large skillet over medium heat.

Brown the meatballs in the hot fat or oil, turning frequently to ensure even browning on all sides.

Remove the browned meatballs from the skillet and set aside.

Prepare gravy in the same skillet (details not provided, assume a roux-based gravy).

Return the meatballs to the skillet with the gravy.

Simmer the meatballs in the gravy for 15 to 20 minutes, or until they are cooked through and the gravy has thickened.

Serve hot.