Bring a large pot of well-salted water to a boil. Cook rotini until al dente according to package directions. Reserve 1/2 cup pasta water, then drain and set aside.

Pat chicken dry and season on both sides with kosher salt and black pepper.

Heat olive oil and 2 tablespoons butter in a large skillet over medium-high heat. Sear chicken 5–6 minutes per side, until golden brown and cooked through (165°F). Transfer to a cutting board to rest.

Reduce heat to medium. If the skillet looks dry, add the remaining 1 tablespoon butter. Stir in minced garlic and cook 30–60 seconds until fragrant, scraping up browned bits.

Pour in heavy cream and bring to a gentle simmer. Gradually whisk in Parmesan until fully melted and the sauce is smooth and glossy.

If the sauce becomes too thick, stir in splashes of reserved pasta water until it coats the back of a spoon.

Add the drained rotini and toss to coat every spiral in the sauce.

Slice the rested chicken into strips or bite-size pieces and fold into the pasta (or serve over the top). Stir in parsley, taste, and adjust salt and pepper as needed.

Garnish with additional parsley and serve immediately while hot and creamy.