Cook Pasta: Begin by bringing a large pot of salted water to a rolling boil. Add pasta and cook according to package instructions until al dente, about 8-10 minutes. Reserve one cup of pasta water, drain the rest, and set pasta aside.

Sauté Chicken: In a large skillet, melt a tablespoon of butter over medium heat. Season diced chicken with salt and pepper, add to skillet, and cook for 6-8 minutes until golden brown and cooked through. Remove chicken and set aside.

Make Sauce: In the same skillet, add another tablespoon of butter, then sauté onion and minced garlic for 3-4 minutes until onion is translucent. Pour in heavy cream and chicken broth, stirring to combine, then add Italian seasoning and red pepper flakes. Simmer for about 5 minutes until thick.

Combine: Add cooked chicken and pasta back into skillet, tossing until well coated. Add reserved pasta water if too thick, cooking for an additional 2 minutes.

Serve: Remove from heat and top with grated Parmesan cheese and parsley. Serve warm.