Heat the olive oil in a large heavy pot or Dutch oven, such as Le Creuset, over medium heat.
Add the onion and saute for 7 minutes, stirring occasionally, until tender.
Add the sausage and cook for 7 to 8 minutes, crumbling it with a fork, until nicely browned. Add the garlic, crushed fennel seeds, red pepper flakes, 1 teaspoons salt, and 1 teaspoon black pepper and cook for one minute.
Pour in the wine, bring to a boil, and add the heavy cream, half-and-half, and tomato paste. Bring back to a boil, lower the heat, and simmer for 20 minutes, until the sauce has thickened.
Meanwhile, bring a large pot of water to a boil, add 2 tablespoons salt, and cook the pasta according to the directions on the package. Drain and add to the sauce, stirring to coat the pasta. Cook over low heat for 5 minutes to allow the pasta to absorb the sauce.
Off the heat, stir in the parsley and 1/2 cup of the Parmesan. Season to taste.
Serve hot in shallow bowls with the remaining 1/2 cup Parmesan on the side.