In a large frying pan, cook the onions until soft, then add the beef and brown gently. Stir in garlic and Worcestershire Sauce and cook for a couple of minutes.
Place beef mixture in a large slow cooker, and add tomatoes, tomato paste, water/stock, garlic, sugar and herbs. Stir well.
Cook on high for 3 hours, or low for 6 hours.
Taste and season with salt and pepper.
Add dried pasta (no need to precook) and give it a good stir, to coat every bit of pasta.
Cover and continue cooking for a further 30 minutes (high) or 45 minutes (low). Check and stir halfway through.
Chop the first mozzarella ball and stir it into the pasta, so it is well distributed. Chop the second mozzarella ball, and scatter it over the top.
Cook for a further 5-10 minutes until mozzarella has melted.
Serve in bowls with optional sprinkling of parmesan.