Put the minced beef, onion, tomato purée and dried mixed herbs in a food processor, season well with salt and pepper and blend until smooth. Shape the mixture into 12 balls, cover and chill for 30 minutes.
Meanwhile, put the tomato sauce ingredients in a saucepan and cook, uncovered, over a low heat for 15–20 minutes, stirring occasionally.
Season the sauce with salt and pepper and transfer to an ovenproof dish. Arrange the meatballs on top and place in a preheated oven, 180°C (350°F), Gas Mark 4, for 45 minutes. Sprinkle the meatballs with chopped parsley and paprika, garnish with parsley sprigs and serve with mashed potatoes, if liked (remembering to count the extra calories).