Heat a 12-inch deep skillet over medium-high heat and add 1 tablespoon olive oil until shimmering.

Add 1 pound bulk Italian sausage, break into pieces, and let sit 2–3 minutes to sear, then stir and cook until mostly browned, about 5–6 minutes; transfer sausage to a bowl and leave fond in the pan.

Reduce heat to medium, add the diced onion and cook 3–4 minutes until translucent, then add the minced garlic and cook 30 seconds until fragrant.

Pour in 1/2 cup chicken broth to deglaze the pan, scraping up browned bits, then stir in 14 ounces crushed tomatoes, 1 teaspoon Italian seasoning, 1/2 teaspoon black pepper, and 1/2 teaspoon kosher salt.

Add 2 1/4 cups chicken broth and bring to a gentle simmer, then stir in 12 ounces uncooked rigatoni and return the browned sausage to the pan; cover and simmer on medium-low for 10 minutes, stirring once halfway through.

Remove the lid, temper 1/2 cup heavy cream with a few spoonfuls of hot sauce from the pan, then stir the tempered cream into the skillet and simmer uncovered for 3–5 minutes until sauce is glossy and rigatoni is al dente.

Stir in the 4 cups of baby spinach in batches until wilted, then remove from heat and stir in 1/2 cup grated Parmesan and 1 tablespoon chopped fresh basil if using; let rest 2 minutes before serving.

Taste and adjust seasoning, adding extra salt, pepper, or a splash of broth if needed.