Prep the sausage and aromatics: Slice the smoked sausage into rounds. Dice the onion and mince the garlic. Grate the Parmesan so it melts smoothly.

Brown the sausage: Heat the olive oil or butter in a large, deep skillet over medium-high heat. Add the sausage and cook 3–4 minutes per side until lightly browned. Remove to a plate, leaving any flavorful drippings in the pan.

Soften the onion: Reduce heat to medium. Add the onion with a pinch of salt. Cook 3–4 minutes until translucent, scraping up browned bits. Stir in the garlic and cook 30 seconds until fragrant.

Toast tomato paste (optional): Stir in the tomato paste and cook 1 minute to deepen the flavor and color.

Add liquids and pasta: Pour in the chicken broth and bring to a lively simmer. Stir in the Italian seasoning and crushed red pepper flakes. Add the pasta, stirring so it doesn’t stick. Return the browned sausage (and juices) to the pan.

Simmer until al dente: Cook uncovered, stirring occasionally, 10–12 minutes or until the pasta is just al dente and much of the broth is absorbed. If the liquid reduces too quickly, add a splash of broth or water.

Make it creamy: Lower the heat. Stir in the heavy cream and simmer gently 2–3 minutes. The sauce should coat the pasta without being soupy.

Add cheese and greens: Remove the pan from heat. Stir in the Parmesan until melted and smooth. Fold in the spinach and let it wilt in the residual heat, 1–2 minutes.

Season and serve: Taste and adjust with salt and black pepper. Finish with chopped parsley and extra Parmesan. Serve hot.