Clean and wash the carrots and celery and cut them into small cubes. Peel onion and garlic. Finely dice the onion, press the garlic through a garlic press. Wash the chilli pepper, cut lengthwise and remove the seeds.
Cut the chili into fine rings. Heat the oil in a pot, fry the onion and garlic in it. Add carrots and celery, steam briefly and salt. Stir in tomato paste and chili, add stock and bring to the boil.
Cover and simmer for about 5 minutes. Wash the tomatoes, drain and cut in half. Put them into the pot together with the tomato sauce and cook for another 5-6 minutes. Put the spaghetti in plenty of boiling salted water and cook for about 8 minutes until bubbly.
Wash the basil, dab dry and cut into fine strips. Season tomato sauce with salt and stir in half of the basil. Pour the pasta onto a sieve, rinse under cold water and drain.
Arrange spaghetti and tomato sauce on a deep plate. Serve sprinkled with remaining basil.