01 - Bring a large pot of generously salted water to a rolling boil. Cook the pasta according to package instructions until al dente. Drain, reserving 1/2 cup of pasta water for the sauce.
02 - Butterfly the chicken breasts for even cooking. Season both sides thoroughly with salt, pepper, and dried Italian herbs if desired.
03 - Heat olive oil in a large skillet over medium-high heat. Place chicken in the skillet and sear until golden brown and fully cooked, approximately 5 to 6 minutes per side. Transfer cooked chicken to a plate and tent loosely to rest.
04 - Reduce the skillet heat to medium. Melt unsalted butter, then add chopped onion. Sauté until softened, about 2 to 3 minutes. Add minced garlic and cook until fragrant, about 1 minute.
05 - Pour in chicken broth, deglazing the skillet by scraping up browned bits to enhance flavor.
06 - Stir in heavy cream and bring mixture to a gentle simmer. Add Parmesan cheese and stir until the sauce is smooth and velvety. Adjust seasoning with additional salt and pepper if needed.
07 - Slice rested chicken breasts thinly. Return chicken to the skillet with sauce, add cooked pasta, and toss thoroughly. Gradually add reserved pasta water to adjust sauce consistency as desired.
08 - Fold in chopped parsley and serve immediately. Garnish with additional parsley and freshly grated Parmesan cheese.