BRING a large pot of water to a boil.
COOK the pasta according to package directions.
ADD the olive oil then brown the sausage and red pepper flakes in a large skillet over medium heat until browned.
ADD onion and garlic.
COOK until the onion is tender.
ADD the tomatoes and heavy cream.
SIMMER until the mixture thickens, about 10 minutes.
ADD the spinach and cook for an additional 3 minutes.
ADD the cooked pasta to the sauce.
SPRINKLE with parmesan, if desired.