Bring a large pot of salted water to a rolling boil. Add the penne pasta, cooking until al dente, about 8-10 minutes. Reserve 1 cup of pasta water before draining the pasta.

In a large skillet, heat olive oil over medium-high heat. Add Italian sausage, breaking it up as it cooks. Sauté until browned, about 5-7 minutes.

Add finely diced yellow onion to the skillet and sauté for about 3-4 minutes until softened. Stir in minced garlic and cook for an additional 1-2 minutes.

Add tomato paste to the skillet and cook for about 1 minute. Pour in crushed tomatoes, Italian seasoning, red pepper flakes, salt, and black pepper. Let simmer for 4-5 minutes.

Reduce heat to low and slowly stir in heavy cream. Let it simmer gently for 2-3 minutes without boiling.

Sprinkle in grated parmesan cheese, stirring until it melts completely and integrates into the sauce.

Add the cooked penne pasta to the skillet, tossing to coat with the sauce. Gradually add reserved pasta water until the desired consistency is reached.

Remove from heat, taste for seasoning, and serve, garnishing with fresh parsley or basil.