Bring a large pot of water to a boil, salt it and cook the pasta according to the directions on the package. Reserve 1-2 cups of pasta water before draining.
Meanwhile, heat the olive oil in a large, deep pan or Dutch oven and cook the sausage for 4-5 minutes over medium heat, breaking them down a bit with your spoon as you go.
Add the onion, garlic and red chili flakes and cook for 2-3 more minutes, stirring often, until the onion becomes translucent.
Stir in the crushed tomatoes and Italian seasoning mix and allow the sauce to bubble for a couple of minutes.
Add the half and half (single cream) and simmer for 1 minute to allow the sauce to thicken a bit.
Lower the heat and stir in the cooked pasta, adding a bit of the reserved pasta water if needed.
Stir in the grated Parmesan and fresh parsley, season to taste and serve immediately.
