Squeeze lots of tiny chunks from the sausages, then wet your hands and roll them into meatballs. I usually get around 8 or so from 1 sausage.
Add a drizzle of oil to a large deep oven-safe pot or pan over medium-high heat. Add the meatballs and fry until they've built up a deep golden crust all over. Remove from the pan and place to one side. Work in batches if you need to and add a drizzle of oil in between if the pan dries out.
Lower the heat to medium and add the shallots to the leftover fat. Fry for a few mins until soft and golden, then add in the garlic & rosemary and fry for a further 30 seconds or so. Stir in the tomato puree and fry for 1 min, then pour in the crushed tomatoes. Fill each can about 1/3 the way up with water, swill then add that in too.
Add in chicken stock, pasta, meatballs, basil and a pinch of salt & pepper. Give it all a good stir, bring to a simmer then lower the heat slightly. Simmer and stir until the pasta cooks right through and the sauce is thick and no longer watery (see video for consistency).
Turn off the heat and stir through 2/3 of the parmesan until it fully blends, then check for seasoning and adjust with salt & pepper. Top with mozzarella and the rest of the parmesan, then place under the grill until deep golden and bubbly. Serve up and enjoy!