Cook pasta as per packet instructions. It should take about 12 minutes. Don't overcook, better to keep al dente.
While pasta is boiling, fry onion in a little olive oil in large, deep frying pan, add garlic. Then add sausage meat and brown, breaking up well - use a masher if you need to.
Drain pasta. Add cream and tomato paste to frying pan and stir to incorporate. Add drained pasta and stir gently.
Stir through parmesan, squeeze over lemon, season well, and sprinkle with chopped parsley and extra parmesan to serve if desired.