Begin by bringing a large pot of salted water to a rolling boil. Once boiling, add 12 ounces of penne pasta and cook according to package instructions until al dente, typically about 8-10 minutes. Reserve 1/2 cup of pasta water before draining the pasta.

In a large skillet, heat 1 tablespoon of olive oil over medium-high heat. Add 1 pound of Italian sausage to the pan and brown it for 6-8 minutes, stirring occasionally until it's no longer pink.

Add the finely diced onion to the skillet and sauté for 3-4 minutes until translucent. Then stir in 4 minced garlic cloves, cooking for an additional 30 seconds until aromatic.

Stir in 2 tablespoons of tomato paste and cook for about 1 minute. Add the crushed tomatoes along with the Italian seasoning, optional red pepper flakes, salt, and black pepper. Let simmer for 4-5 minutes until thickened.

Lower the heat and gradually stir in 1 cup of heavy cream, heating for about 3 minutes until smooth and creamy.

Fold in 3/4 cup of grated parmesan cheese, stirring until completely melted and blended into the sauce.

Add the drained pasta into the skillet, tossing thoroughly to coat with the sauce. Gradually mix in the reserved pasta water until the sauce reaches your desired consistency.

Adjust seasoning as needed, adding more salt or red pepper flakes for heat. Sprinkle with chopped parsley or basil before serving.