Cook the penne pasta in a large pot of salted boiling water according to package directions.

While the pasta is cooking, heat the olive oil in a large skillet over medium-high heat.

Cook the Italian sausage along with the onion, garlic, red pepper flakes, and salt until the sausage is no longer pink.

Drain excess fat from the skillet if necessary and return the meat mixture to the pan.

Turn the heat to low and add the cream to the skillet. Bring to a simmer and add in the spinach.

Cook, stirring for about 3 minutes until the spinach is wilted.

Stir in the Parmesan cheese until melted. Stir the pasta into the sauce.

Serve immediately