Pour the tomatoe paste in a medium, heavy-based saucepan over low-medium heat. Add the onion, carrots and celery.
Pour the olive oil and bring to the boil.
Decrease the heat to low and gently simmer for 30 minutes.
Stir in the basil leaves and season with salt and pepper.
Meanwhile, bring a large pot of water to the boil. Add a tsblespoon of salt and a splash of oil. Cook the pasta according to the packet directions, until al dente. Drain and put in a large serving bowl.
Pour sauce over the pasta and toss to combine. Add the mozzarella and toss to coat. Served topped with parmesan. Serves hot!