Bring a large pot of salted water to a rolling boil. Add the pasta and cook according to the package instructions until al dente (typically 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 the diced chicken pieces, season with salt and pepper, and cook for about 6-8 minutes until golden brown and cooked through. Remove the chicken and set aside.

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

Pour in the heavy cream and chicken broth, stirring to combine. Add the Italian seasoning and red pepper flakes. Let the sauce simmer gently for about 5 minutes until it thickens slightly. Use the reserved pasta water to adjust if it gets too thick.

Return the cooked chicken and drained pasta to the skillet with the sauce. Adjust seasoning with additional salt and pepper if needed. Toss everything together to ensure the chicken and pasta are coated. Cook for another 2 minutes.

Sprinkle grated Parmesan cheese over the top and let it melt into the dish. Garnish with fresh parsley before serving.