We make this at the cookery school quite a bit ,and people always love it. Just leave out the sausage for a vegetarian pasta sauce. It also freezes well.
Melt the butter in a large saucepan, add the chopped tomatoes, garlic and rosemary.
Season with salt, pepper and sugar ( the sugar really helps the tomatoes).
Cook until the tomatoes have just begun to soften, about 5 mins.
Add the sausage to the pan with the chilli flakes, cream and half the chopped parsley,
Allow to simmer with the lid off until the mixture has reduced by half, stirring frequently.
Take off the heat and taste for seasoning.
Cook the pasta in a large pot of boiling water, into which you have added 1 dst salt, until it is just cooked, then drain and toss with the sauce.
Put into a great big serving bowl and scatter with the grated parmesan cheese and the rest of the parsley.
NOTE FOR COOKING PASTA: If you need to cook your pasta slightly ahead of time,keep about 50ml of the pasta cooking water in with the pasta and a good glug of olive oil.