Prepare the garlic and the chili pepper as described above and put them into a cold skillet with the oil and a few parsley stems. Slice the pepper or leave it in one piece, according to your taste.
Cook it for one minute until hot and then remove it from the heat; let cool down. Put the pan over the heat and cook until warm again; let cool down. Repeat this process three times: this operation will allow the garlic and pepper to release their full aroma.
Remove the parsley to prevent any bitter aftertaste in the sauce.
Crush the peeled plum tomatoes with a masher and add them to the skillet when the oil has cooled down.
Cook this mixture over low heat until it boils.
Simmer for about 15 minutes until the sauce thickens. Stir occasionally.
Season with salt to taste.
In the meanwhile, cook the pasta in plenty of salted water.