Peel and finely chop the onion and garlic.
Heat up the oil in a frying pan, then add the chopped onion. Fry for about 5 minutes on a medium heat.
Meanwhile, wash the basil and put a few leaves aside for later. Chop up the rest (both leaves and stalks).
Add the chopped garlic and basil and fry for a couple of minutes, then add the tinned tomatoes. To help get all the tomato sauce out, add a tiny bit of water to the tin, swish it around then and empty the tomato water into the pan.
Grind in a little salt and pepper then leave the sauce to cook for about 15 minutes, mixing occasionally with a wooden spoon. After the time has passed, use the spoon to break up the tomatoes more thoroughly.
Serve with your favourite pasta and garnish with the basil leaves that you put aside earlier.