01 - Bring a large pot of salted water to a boil. Add fettuccine or linguine and cook according to package instructions until al dente. Drain pasta, reserving 1/2 cup of the cooking water.
02 - Butterfly chicken breasts. Season both sides with salt, freshly ground pepper, and Italian herbs if desired.
03 - In a large skillet over medium-high heat, add olive oil. Sear chicken breasts until golden brown and cooked through, approximately 5 to 6 minutes per side. Transfer chicken to a plate, cover loosely, and let rest.
04 - Reduce skillet heat to medium. Add unsalted butter. Sauté chopped onion for 2 to 3 minutes until softened. Add minced garlic and cook until fragrant, about 1 minute.
05 - Pour in low-sodium chicken broth and deglaze the skillet, scraping up browned bits for added flavor.
06 - Add heavy cream to the skillet, bringing to a gentle simmer. Stir in grated Parmesan cheese until the sauce is smooth and creamy. Adjust seasoning with additional salt and pepper as needed.
07 - Slice rested chicken breasts thinly. Return chicken to the skillet along with the cooked pasta. Toss thoroughly, adding reserved pasta water as needed to achieve desired sauce consistency.
08 - Stir chopped parsley into the pasta. Serve immediately, garnishing with extra parsley and Parmesan cheese.