For the meatballs, mix breadcrumbs and milk. Finely grate the parmesan. Peel and chop 1 onion and garlic. Knead minced meat, breadcrumbs, egg, onion, mustard, Parmesan cheese, herbs, 1 level tsp salt and 1⁄2 tsp pepper.
Form meatballs. Heat 2 tablespoons of oil in a large ovenproof pan. Fry the meatballs for 6-8 minutes on each side.
For the tomato sauce peel 1 onion and dice finely. Remove the meatballs from the pan. Wipe the pan with kitchen paper. Heat 1 tablespoon of oil and sauté the onion. Add the tomatoes, chop a little and bring to the boil.
Simmer for about 10 minutes. Season to taste with salt, pepper, 1 teaspoon sugar and vinegar. In the meantime, preheat the oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Cut mozzarella into thin slices.
Place the meatballs in the sauce, spread the cheese on top and bake in a hot oven for about 15 minutes. Served with noodles.