01 - Bring a large pot of salted water to a boil. Cook pasta according to package instructions until al dente. Drain pasta, reserving 1/2 cup of the cooking water.
02 - Butterfly chicken breasts and season both sides generously with salt, freshly ground pepper, and dried Italian herbs if using.
03 - Heat olive oil in a large skillet over medium-high heat. Add chicken and sear each side until golden brown and fully cooked, about 5 to 6 minutes per side. Transfer chicken to a plate, cover loosely, and allow to rest.
04 - Reduce skillet heat to medium. Add butter, then onion; sauté until softened, 2 to 3 minutes. Add minced garlic and cook, stirring, until aromatic, about 1 minute.
05 - Deglaze pan with chicken broth, scraping up any browned bits with a wooden spoon.
06 - Add heavy cream and bring to a gentle simmer. Stir in Parmesan cheese until sauce is smooth and velvety. Season with additional salt and pepper to taste.
07 - Thinly slice rested chicken. Return chicken and cooked pasta to the skillet. Toss thoroughly to combine, adding splashes of reserved pasta water as needed to achieve desired sauce consistency.
08 - Stir in chopped parsley. Serve immediately, topped with extra fresh parsley and more Parmesan if desired.