Bring a large pot of salted water to a vigorous boil over high heat. Add your choice of pasta and cook until al dente, usually around 8-10 minutes. Reserve 1 cup of starchy pasta water, then drain and set aside.

In a large skillet, melt 2 tablespoons of butter over medium heat. Season the diced chicken breast with salt and pepper and cook for about 6-8 minutes until golden brown and cooked through. Remove and set aside.

Using the same skillet, add remaining butter and let it melt. Add minced garlic and diced onion, sauté for 3-4 minutes until translucent and aromatic.

Pour in heavy cream and chicken broth, stirring well. Add Italian seasoning and red pepper flakes. Simmer gently for about 5 minutes until thickened, adjusting with reserved pasta water as needed.

Return sautéed chicken and cooked pasta to the skillet. Mix thoroughly, ensuring everything is well-coated. Cook for an additional 2 minutes.

Remove from heat and sprinkle grated Parmesan cheese on top. Garnish with chopped parsley before serving.