In a large Dutch oven, heat olive oil on medium heat.
Add the fennel bulb and onion and sauté for 7-10 minutes. Stir occasionally or at least once a minute.
Add in the sausage and cook until well-browned or for nearly another 10 minutes at medium-high heat.
Mix in the garlic, crushed fennel seeds, red pepper flakes, salt and black pepper. Cook for 1 minute.
Pour in the heavy cream, half-and-half, and tomato paste. Combine ingredients.
Bring contents to a boil, reduce heat to low and simmer for 20 minutes or until the sauce has thickened.
Meanwhile, bring a large pot of salted water to a boil, and cook rigatoni according to the directions on the package. Drain pasta and add it to the sauce, stirring to coat all of the rigatoni.
Cook on low for 5 minutes to allow the pasta to absorb the sauce.
Remove from heat and stir in the parsley and 1/2 cup of Parmesan cheese. Serve pasta and top with remaining Parmesan cheese.
Enjoy!