Peel and finely slice the garlic and chilli (halve and deseed it first, if you don’t want the sauce too hot).
Pick the basil leaves off the stalks and put to one side. Finely chop the stalks.
Cook the spaghetti according to packet instructions.
Meanwhile, put a large saucepan on medium heat and add the oil. Add the garlic, chilli and basil stalks and give them a stir.
When the garlic begins to brown slightly, add most of the basil leaves and tomatoes. Turn the heat up high and stir for 1 minute. Taste and season with salt and pepper, if needed.
Drain the spaghetti, reserving a mugful of cooking water, then transfer it to the pan of sauce and stir well. Add a splash of pasta cooking water to loosen, if needed, then taste and season to perfection.
Put the pasta in a large serving dish. Roughly tear over the remaining basil leaves and finely grate over the Parmesan.