Clean and finely chop the onions (you will probably cry a little!) .Heat the oil in a frying pan, add the chopped onion and cook slowly until it becomes a sort of cream (take care not to let it burn, adding 1or 2 spoonfuls of hot water if necessary). Now add the chopped tomatoes, a pinch of salt, the sugar and the chopped chilli pepper (or even 2, if you prefer a spicier sauce). Leave to simmer over a low heat for another 15-20 minutes. Cook the spaghetti in boiling, salted water until “al dente”; then strain and toss them in the pan with the hot sauce.
Serve them sprinkled with plenty of tasty, grated Tuscan pecorino.