Begin by bringing a large pot of salted water to a boil. Add the fusilli bucati and cook according to package instructions until al dente. Reserve 1 cup of the pasta cooking water, then drain the pasta and set it aside.
In the same pot (or a large skillet), heat the olive oil over medium heat. If using, add the finely diced onion and sauté for about 2-3 minutes, until translucent. Stir in the minced garlic and cook for an additional 30 seconds until fragrant.
Add the tomato paste to the pan, stirring it into the onions and garlic until well combined. Cook for about 2 minutes to deepen the flavor.
Pour in the heavy cream and chicken stock, stirring continuously until the mixture is smooth and heated through. If you like a bit of heat, sprinkle in the red pepper flakes at this stage.
Add the cooked fusilli bucati to the sauce, along with the reserved pasta cooking water. Toss everything together until the pasta is thoroughly coated in the creamy tomato sauce.
Stir in the freshly grated Parmesan cheese, allowing it to melt and integrate into the sauce. Taste and adjust seasoning with additional salt if needed.
Plate the creamy tomato pasta, garnishing with extra Parmesan cheese and a sprinkle of red pepper flakes if desired. Enjoy your meal!