Bring a large pot of salted water to a rolling boil. Add the rotini and cook it according to the package directions until it's al dente. Before draining, scoop out about a cup of the starchy pasta water and set it aside for later.
While the pasta cooks, season your sliced chicken with salt, pepper, and Italian seasoning. Heat olive oil in a large skillet over medium-high heat and sear the chicken pieces for about four to five minutes per side. Remove the chicken once it's golden and fully cooked, then set it aside.
In the same skillet, lower the heat to medium and melt the butter. Add the minced garlic and cook it for about a minute, just until it turns fragrant. Be careful not to let it brown, since burnt garlic turns bitter fast.
Pour in the chicken broth and let it simmer for a minute to pick up all the flavorful bits from the pan. Stir in the heavy cream and bring it to a gentle simmer, letting it thicken slightly for about three minutes.
Lower the heat and slowly whisk in the grated parmesan, a handful at a time. Stirring constantly here keeps the cheese from clumping and helps you get that smooth, glossy sauce texture everyone loves.
Add the drained rotini and seared chicken back into the skillet. Toss everything together so the pasta and chicken are fully coated in the garlic cream sauce, using the reserved pasta water to thin it out if needed.