Bring a large pot of salted water to a rolling boil. Add the fusilli (or penne/rotini) and cook until al dente according to package directions. Reserve ½ cup of the pasta cooking water, then drain the pasta and set aside.

Pat the chicken cubes dry with paper towels and season with fine salt, black pepper, and ½ tsp Italian seasoning. Heat a large skillet over medium-high heat and melt 1 Tbsp of butter. Add the chicken in a single layer and cook for 3–4 minutes per side until golden and cooked through. Transfer to a plate, keeping any pan juices in the skillet.

Lower the heat to medium. Add the remaining 2 Tbsp of butter to the skillet. Stir in the minced garlic and red pepper flakes, cooking for 30–60 seconds until fragrant but not browned.

Pour in the chicken broth, using a wooden spoon to scrape up the browned bits stuck to the pan. Stir in the heavy cream and the remaining ½ tsp of Italian seasoning. Let the sauce simmer gently for 2–3 minutes until it thickens slightly.

Reduce the heat to low and gradually sprinkle in the grated Parmesan while stirring constantly until the cheese fully melts and the sauce becomes smooth. Adjust seasoning with salt and pepper.

Return the seared chicken to the skillet along with any juices. Add the drained pasta and toss everything together until evenly coated in the sauce. If the sauce is too thick, stir in splashes of reserved pasta water. Finish with chopped parsley.