Bring a large pot of salted water to a rolling boil. Add the pasta and cook according to package instructions until al dente (usually 8–10 minutes). Reserve 1 cup of pasta water, then drain and set aside.

In a large skillet, melt 2 tablespoons of butter over medium heat. Add diced chicken pieces and season lightly with salt and pepper. Cook for 6–8 minutes until golden brown and cooked through, stirring occasionally. Remove chicken and set aside.

In the same skillet, add the remaining butter and sauté minced garlic and diced onion until translucent, about 3–4 minutes.

Pour in heavy cream and chicken broth, stirring to combine. Add Italian seasoning and red pepper flakes. Let the sauce simmer gently for about 5 minutes to thicken slightly.

Return chicken and drained pasta to the skillet with the sauce. Adjust seasoning with salt and pepper. Toss to coat evenly and let cook for 2 more minutes to marry flavors and warm through.

Sprinkle grated Parmesan over the top and let it melt into the sauce. Garnish with fresh parsley and serve warm.