Heat 1 tablespoon of olive oil in a large, high-sided, heavy-bottomed skillet over medium heat. Add the crumbled sausage and cook for about 5 minutes, breaking it up with a spoon, until fully cooked with no pink remaining. Drain any excess grease, leaving just enough to coat the pan.

To the same skillet with the sausage, add the uncooked rigatoni, chicken broth, heavy cream, minced garlic, Italian seasoning, and tomato sauce. Stir everything together thoroughly, making sure the pasta is submerged in the liquid.

Bring the mixture to a boil over medium heat, then immediately reduce to a gentle simmer. Cover the skillet with a lid and cook for 10 to 15 minutes, stirring every 3 to 4 minutes to prevent sticking. The pasta should be tender and the sauce noticeably thickened when done.

Stir in the fresh spinach and continue cooking for 1 to 2 minutes, stirring frequently, until the spinach has wilted into the sauce.

Taste and add salt, black pepper, and red pepper flakes according to your preference.

Serve hot, topped with shredded Parmesan cheese if desired.