Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the pasta and set aside.

In a large skillet, heat the olive oil over medium heat. Add the Italian sausage and cook, breaking it up with a spoon, until browned and cooked through, about 5-7 minutes.

Add the minced garlic to the skillet and cook for an additional 1-2 minutes until fragrant.

Reduce the heat to low and pour in the heavy cream, stirring to combine. Let it simmer for 2-3 minutes until slightly thickened.

Stir in the grated Parmesan cheese until melted and smooth. If the sauce is too thick, gradually add some reserved pasta water until desired consistency is reached.

Add the cooked penne pasta to the skillet, tossing to coat the pasta evenly with the sauce. Season with red pepper flakes (if using), salt, and black pepper to taste.

Serve immediately, garnished with chopped fresh parsley.