To make the sauce, heat 1 tbsp oil in a non-stick trying pan. Add the sausage and cook, breaking it up as it browns, so you have quite small pieces. Add the garlic, fennel and rosemary and cook for a couple of minutes.
Heat the oven to 190C/fan 170C/gas 5. Add the tomatoes then simmer for 20 minutes until thickened. Cook the pasta but keep an eye on it, and stop cooking when it is a couple of minutes away from being done - you will be cooking it more in the oven so you want it to still have a bit of bite.
Mix the pasta with the sauce and tip into a baking dish. Scatter over the mozzarella and grana padano and bake for 20-30 minutes until bubbling and golden. Serve with a salad, if you like.