Cut the tomatoes in half lengthwise and mix with the oregano, garlic, ¼ tsp salt and 3 tbs olive oil. Pour onto a flat baking tray and roast in a 140°C oven for 40 minutes.
In the meantime, fry the onions in 1 tbs olive oil until soft. As soon as they’re soft, add the tomato paste and fry for a further minute or two (it gets rid of tomato paste’s harsh metallic quality).
Pour the roasted tomatoes into a food processor, add the onions and blitz until pureed. Place the puree in a fine sieve and use the back of a spoon to push it through. A wonderful velvety sauce is what emerges and the pips and skins stay behind. Put the tomato sauce back on the heat and stir through the mascarpone. If the sauce is a bit too thick for your liking, add a few drops of the water you boiled your pasta in. Just before serving, add the red wine vinegar, a grinding of black pepper and salt, if needed. Serve with a pasta of your choice, purple basil (I love the purple against the red) and fresh parmesan.