Cook the pasta in salted boiling water in a medium sized pot according to the package directions until al dente according to package instructions. (Usually about 9 minutes.) Strain and set aside when finished cooking, keeping ¼ cup of the starchy water the pasta cooked in.
While the pasta is cooking, melt the butter in a large, deep skillet over medium heat. Add the onion and cook until soft about 2-3 minutes.
Place the sausage in the skillet, removing the casing if using links. Cook the sausage with the vegetables until cooked through and no longer pink, about 5-7 minutes over medium high heat. Add the garlic and cook until fragrant, about a minute.
Add the flour to the sausage, sprinkling it evenly. Cook for about 30 seconds over medium high heat then turn the heat to medium-low. Add the chicken broth, Italian seasoning and pepper. Stir the mixture well to deglaze the pan.
Turn the pot to low. Pour the pasta water into the pan, followed by the heavy cream. Slowly bring the mixture to a gentle simmer until you reach medium high heat, then reduce the heat until the sauce is just simmering. Simmer the sauce for about 4-6 minutes, stirring occasionally.
Add the parmesan cheese to the sauce a little at a time, stirring well until it is fully mixed into the sauce. Combine the sauce with the cooked pasta and stir well until the pasta is fully covered. (see notes)
Add the chopped spinach and stir for about a minute until it wilts while the pasta is still hot, then serve and enjoy!
Notes
Tips For Mixing The Sauce With The Pasta
If your skillet isn't a deep, large pan you may have to transfer the pasta and sauce to a large bowl to mix. This is totally ok! Just add the spinach while the sauce is still piping hot so the spinach wilts a little in the dish and enjoy!If you waited too long and you feel the pasta and sauce has cooled too much before adding the spinach, you can cook the spinach just enough to cook it in a skillet before adding it to the pasta.
Can I Use Frozen Spinach?
You can use frozen spinach, but will need to heat it up in a separate skillet to remove the excess water from it before adding it to the pasta. Frozen spinach will not warm up enough adding it straight to the pasta, and the excess water in frozen spinach can make the pasta sauce too runny.You can also microwave the spinach in a bowl to defrost and warm it up. You will need to drain off the excess water. I recommend drying the spinach also well with paper towels so the cheese sauce does not become too runny.