In a non-stick frying pan, warm the olive oil over low heat. Add the chopped onion and cook slowly covered, for 5 minutes, or until soft and translucent. Add the tomatoes, then cook, uncovered, for 20 minutes, stirring occasionally until thick and pulpy.
In a non-stick frying pan, heat the oil, then add the butter over high heat. When it has melted and is sizzl