For the tomato sauce, wash and coarsely dice the tomatoes. Peel and finely dice the onion. Heat 1 tablespoon of oil in a pot, not too hot. Sauté the onion briefly until transparent. Add tomatoes and tomato paste.
Season with salt, pepper and sugar. Bring to the boil and simmer covered for about 20 minutes.
Peel garlic and chop finely. Puree the sauce finely and pass through a sieve. Add garlic, bring sauce to the boil again and simmer for 1-2 hours. The sauce should become thicker and lighter. If it gets too thick, stir in some water.
Season again with salt and pepper.
Cook the pasta in 3-4 l boiling salted water (1 teaspoon salt per litre) according to the instructions on the packet. Drain tuna and sardines.
Peel and finely dice the red onion. Heat 1 tablespoon of oil and fry the diced onion in it. Add tuna, sardines and tomato sauce and bring to the boil again.
Parmesan cheese in shavings. Wash the basil, shake dry, pluck the leaves from the stalks and cut into small pieces. Drain the pasta and put it back into the pot. Fold through with the tomato sauce and a little basil.
Season again, then serve. Sprinkle with the rest of the basil and parmesan.