Cook the Pasta
Bring a large pot of salted water to a boil. Cook rigatoni until al dente. Reserve ½ cup pasta water, then drain.
Brown the Sausage
Heat olive oil in a large skillet over medium-high heat. Add sausage and cook until browned and slightly crispy. Remove and set aside.
Build the Flavor Base
In the same skillet, add butter and onion. Cook until soft. Stir in garlic and cook until fragrant.
Make the Cream Sauce
Pour in heavy cream, Italian seasoning, and red pepper flakes. Simmer gently until slightly thickened.
Combine
Return sausage to the skillet. Add cooked pasta and toss to coat. Add pasta water as needed.
Finish
Stir in Parmesan cheese until melted and creamy. Season with salt and pepper to taste.
Serve
Garnish with fresh herbs and serve immediately.