Heat the olive oil in a stockpot. Add the onion and garlic, and sauté until they soften and are just beginning to turn golden. Add the tomatoes, chilli and basil, and cook for about 15 minutes until the tomatoes have melted into a sauce. Mash them up with a wooden spoon if necessary.
Add the potatoes, season with salt and pepper and, with a wooden spoon, stir to coat them. Add about 4 c