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, drain, and set aside.

In a large skillet, melt 2 tablespoons of butter over medium heat. Add the chicken and season with salt and pepper. Cook for about 6-8 minutes until golden brown. Remove from skillet and set aside.

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

Pour in the heavy cream and chicken broth, stirring to combine. Add Italian seasoning and red pepper flakes. Simmer for about 5 minutes until slightly thickened. Adjust the consistency with reserved pasta water if necessary.

Return the chicken and pasta to the skillet, adjusting seasoning with salt and pepper. Toss to coat and cook for another 2 minutes.

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