Salsa con aglio e cipolla (Garlic and onion sauce)

Kg. 1 tomatoes for sauce,
3 garlic cloves,
1 onion,
basil,
olive oil,
salt and pepper.

Cook chopped tomatoes, sliced onions, chopped garlic, basil and salt for 20 minutes on a low flame. When ready, sieve.

Put sauce back in a pan, dress with oil, pepper and if necessary some salt and cook for about 10 minutes.