Finely chop the onion. Next, gently rinse the basil leaves and delicately pat them dry. If you rub the leaves, instead of patting them dry, they will loose part of their aroma.
Wash and dry the tomatoes. Next, using a paring knife, remove the eye from each tomato.
Using a paring knife, score a cross on the bottom of each tomato.
Take a large pan full of water, bring the water to the boil, plunge the tomatoes into the pan and blanch for 15-20 seconds, until you see some cracks on the tomato skin. I had 10 tomatoes, so I did this in two stages (don’t add all the tomatoes into the boiling water in one go; it will bring the temperature of the water down and make the blanching less effective).
Using a slotted spoon, remove the tomatoes from the pan.
Put the tomatoes into a colander.
Peel the tomatoes.
Quarter the tomatoes.
Remove core and seeds from each tomato quarter. The pictures shows a small bowl on the left, where I have collected all the cores and seeds. These will not be of any use so you can discard them. Keep only the tomato petals.
Dice the tomato petals.
Put the olive oil into a sauce pan. Heat the oil and then add the onion.
Sweat the onion off over medium heat, until it colours (3-4 minutes will be sufficient).
Next, add the diced tomato into the pan.
Stir for few seconds.
Cover the pan with a lid, bring the heat to low and let cook for 10 minutes.
After 10 minutes remove the lid and add the sugar. At this stage you can also add the tomato purée, if you have chosen to use it. Give it a good stir and simmer on a very gentle heat for 30 minutes. Leave the pan uncovered because during this time the sauce has to be brought to the right consistency (a thin sauce will not coat the pasta properly!).
10 minutes before the finish, taste the sauce and season with salt according to taste.
2 minutes before the finish, add the basil leaves.
Give the sauce a final sir.
When the 30 minuets cooking time has elapsed, remove the pan from the heat. Finish the sauce by adding a dash of olive oil and set aside until the spaghetti are ready.
Boil the spaghetti according to the instruction given on the packet. Spaghetti should be cooked “al dente” (firm to the bite).
Once the spaghetti are ready, drain the spaghetti e toss them into the previously prepared tomato sauce (traditionally, Italians top their pasta with only enough sauce to coat the pasta). Finish the dish with a generous sprinkle of Parmesan or Pecorino cheese.