Bring a large pot of salted water to a rolling boil. Cook the pasta according to package instructions until al dente, about 8-10 minutes, reserving 1 cup of pasta water before draining.

In a large skillet, melt 2 tablespoons of butter over medium heat. Add diced chicken pieces and season with salt and pepper. Cook for 6-8 minutes or until golden brown and fully cooked. Set aside, keeping the skillet for the next steps.

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

Pour in heavy cream and chicken broth, stirring to combine. Add Italian seasoning and red pepper flakes, letting it simmer for about 5 minutes until it slightly thickens. Adjust with reserved pasta water if necessary.

Add the cooked chicken and drained pasta back into the skillet, tossing to combine everything well. Allow to cook for an additional 2 minutes. Taste and adjust seasoning if needed.

Sprinkle grated Parmesan cheese over the top and allow it to melt. Garnish with fresh parsley if desired.