Cook the Pasta: In a large pot of salted boiling water, cook the rigatoni according to package instructions until al dente. Drain and set aside.

Brown the Sausage: In a large skillet over medium heat, add the olive oil. Once hot, add the Italian sausage, breaking it up with a spoon as it cooks. Cook until browned and cooked through, about 5-7 minutes.

Sauté the Vegetables: Add the chopped onion to the skillet with the sausage and sauté for about 3-4 minutes, until the onion is softened. Stir in the minced garlic and cook for an additional minute until fragrant.

Create the Sauce: Pour in the heavy cream and marinara sauce, stirring to combine. Add the Italian seasoning, salt, and black pepper. Bring to a gentle simmer and let it cook for 3-5 minutes, allowing the sauce to thicken slightly.

Combine Pasta and Sauce: Add the cooked rigatoni to the skillet and toss until the pasta is well coated in the creamy sausage sauce. Stir in the grated Parmesan cheese until melted and incorporated.

Serve: Remove from heat and garnish with fresh basil or parsley. Serve warm, with additional Parmesan cheese on the side if desired.