Bring a large pot of salted water to a rolling boil. Cook rigatoni pasta for 9 to 10 minutes until just shy of al dente. Reserve 1/2 cup of starchy pasta water before draining.

While pasta cooks, heat 1 tablespoon of sun-dried tomato oil in a deep 12-inch skillet over medium-high heat. Add ground Italian sausage, breaking it up with a wooden spoon into bite-sized crumbles, and cook for 5 to 6 minutes until deeply browned and caramelized. Transfer cooked sausage to a plate, leaving 1 tablespoon of drippings in the skillet.

Reduce heat to medium. Add diced onion to the skillet and sauté for 3 minutes until translucent. Stir in minced garlic, sliced sun-dried tomatoes, Italian seasoning, and red pepper flakes, cooking for 1 minute until aromatic.

Pour in chicken broth to deglaze the skillet, scraping up all the golden-brown caramelized fond from the bottom of the pan. Simmer for 2 minutes until liquid reduces by half.

Lower heat to medium-low and pour in heavy cream. Bring to a gentle simmer for 3 minutes until slightly thickened. Stir in freshly grated parmesan cheese until melted and velvety smooth.

Return the browned Italian sausage to the skillet along with the drained al dente pasta and fresh baby spinach. Toss continuously over low heat for 1 to 2 minutes until spinach wilts into the pasta and the sauce clings luxuriously to every ridge.

If the sauce is too thick, splash in 2 to 4 tablespoons of reserved warm pasta water to achieve a glossy restaurant sheen. Season with salt and cracked black pepper to taste.

Divide among warm shallow pasta bowls. Garnish with freshly shaved parmesan ribbons, torn fresh basil, and serve immediately with warm garlic sourdough bread.