In a large pot, bring salted water to a rolling boil. Add the rigatoni pasta and cook according to the package instructions until al dente. Drain well and set aside, reserving a little pasta cooking water.
In a large skillet over medium heat, add the olive oil and allow it to heat up. Once shimmering, add the Italian sausage and break it into smaller pieces. Cook for about 5-7 minutes until browned and cooked through.
Add the finely chopped onion to the skillet and sauté for approximately 3 minutes until soft and translucent. Then add the minced garlic and cook for another 1-2 minutes until fragrant.
Pour the chicken broth into the skillet and bring to a gentle simmer. Reduce heat to low and stir in the heavy cream and grated Parmesan cheese until smooth and creamy.
Sprinkle in the Italian seasoning and red pepper flakes (if using). Adjust flavor with salt and freshly ground pepper to taste.
Gently fold the cooked rigatoni into the skillet with the creamy sauce, tossing to coat evenly. Cook for an additional 2-3 minutes over low heat, adding reserved pasta water if the sauce is too thick.
Remove from heat, plate the creamy rigatoni, and garnish with torn fresh basil leaves.
Notes
Serve immediately in warm bowls, drizzling extra Parmesan cheese over the top if desired, and pair with a light green salad for a complete meal.