1 Heat the olive oil in a saucepan over medium heat. Add the chopped onions and garlic, then season with salt and pepper. Cook for 5-7 minutes, stirring, until the onion has softened.
2 Add the tomatoes and crush them in the pan with a potato masher to break them up.
3 Rinse each tin out with a 1/4 tin of cold water and add this to the saucepan. Simmer over a low heat, uncovered, for about 40 minutes.
4 Stir in the mascarpone until it melts and the sauce becomes creamy. Taste the sauce and adjust the seasoning as necessary.
5 Mix with the Penne pasta and serve with a few sprigs of fresh basil.