To make the meatballs, mix the minced beef, onion, garlic, breadcrumbs, cheese and chopped parsley together in a bowl until combined. Season well and add the beaten egg to bind, mixing with your hands.
Shape a small piece of the mixture into a ball and fry in an oiled pan until cooked, then taste for seasoning. If necessary, adjust the seasoning of the uncooked mixture. With damp hands, shape the mixture into about 16 meatballs, trying not to press them too tightly. Place on a large plate, cover with cling film and chill for at least 30 minutes.
To cook the meatballs, heat the olive oil in a large, wide pan. Add the chilled meatballs and fry for 5 minutes, turning frequently, until browned all over. Divide the meatballs between warm bowls and sprinkle with sprigs of flat leafed parsley to serve.