Boil a large pot of water and cook the fusilli. Saute onion and garlic in the butter and olive oil over medium heat. Add the crumbled sausage and cook through, about 10 minutes. Add the cream to the pan and sprinkle with salt, pepper (to your liking) and 1 tablepsoon of rosemary, and cook over a simmer for about 5 minutes. Serve over the cooked fusilli and sprinkle with the remaining rosemary and some parmesan cheese. Serve with parmesan alongside.