1. Melt butter, lightly fry rosemary and garlic.
2. Add tinned tomatoes, salt, pepper, sugar and half of the parsley.
3. Simmer over a medium heat for 5 minutes, add thinly sliced chorizo.
4. Stir in cream, and lightly simmer until the sauce is reduced by half - around 40 minutes.
5. Cook pasta in lots of salted water, with a slosh of olive oil in it.
6. Serve sauce over cooked pasta, sprinkled with chopped parsley, and grated parmesan cheese.