Melt the butter in a sauce pan, add chopped rosemary and diced tomatoes.
Season with salt and pepper and sugar.
Cook until the tomatoes have just begun to soften into a sauce, which takes about 5 minutes.
Slice the sausage into 5mm/¼in rounds and add to the pan with the crushed chilies.
Add the cream and two tablespoons of chopped flatleaf parsley, and allow to bubble for 3-4 minutes, stirring frequently until the cream has reduced by half. Remove the pan from the heat and set aside.
Cook the pasta until it is 'al dente', drain and stir into the sauce with the grated parmesan.
Sprinkle with remaining flatleaf parsley, and serve.