01 - Bring a large pot of salted water to a boil. Cook pasta according to package instructions until al dente. Drain, reserving 1/2 cup of pasta water.
02 - Butterfly the chicken breasts and season both sides with salt, freshly ground pepper, and dried Italian herbs if desired.
03 - Heat olive oil in a large skillet over medium-high heat. Sear chicken until golden and cooked through, approximately 5 to 6 minutes per side. Transfer chicken to a plate and cover loosely.
04 - Reduce heat to medium. In the same skillet, add unsalted butter and sauté onion for 2 to 3 minutes until softened. Add garlic and cook until fragrant, about 1 minute.
05 - Pour in chicken broth, scraping up any browned bits from the skillet.
06 - Add heavy cream and bring to a gentle simmer. Stir in Parmesan cheese until the sauce is smooth and creamy. Adjust seasoning with additional salt and pepper as needed.
07 - Thinly slice the rested chicken breasts. Return chicken and cooked pasta to the skillet. Toss with the sauce, adding reserved pasta water gradually to reach desired consistency.
08 - Stir in chopped parsley. Serve immediately, garnished with extra parsley and freshly grated Parmesan cheese.