In a large pot of salted boiling water, cook the rigatoni according to package instructions until al dente. Drain and set aside, reserving about 1/2 cup of pasta water.
In a large skillet over medium heat, add olive oil. Remove the sausage from its casing and crumble it into the skillet. Cook for about 5-7 minutes, until browned and cooked through, breaking it into smaller pieces as it cooks.
Add the chopped onion and minced garlic to the skillet with the sausage. Sauté for an additional 3-4 minutes until the onion becomes translucent and fragrant.
Reduce the heat to low, then stir in the heavy cream and bring it to a gentle simmer. Mix in the grated Parmesan cheese, stirring until melted and creamy.
Add sun-dried tomatoes, fresh spinach, and Italian seasoning to the sauce. Stir until the spinach wilts, about 2-3 minutes. Season with salt and pepper to taste.
Add the cooked rigatoni to the skillet and toss to coat in the creamy sauce. If the sauce is too thick, add reserved pasta water a little at a time until you reach your desired consistency.
Remove from heat and garnish with fresh basil. Serve immediately while hot.
Notes
Feel free to adjust the spice level by choosing mild or spicy sausage.