Bring a large pot of salted water to a boil. Add the rigatoni and cook according to package directions until al dente. Reserve 1 cup of pasta water before draining.

While the pasta cooks, season the cubed chicken with 1/2 teaspoon salt, 1/4 teaspoon black pepper, and Italian seasoning. Heat olive oil in a large skillet over medium-high heat. Add chicken in a single layer and cook for 5-7 minutes, turning occasionally, until golden brown and cooked through. Remove chicken from skillet and set aside.

Reduce heat to medium. Add 4 tablespoons of butter to the same skillet. Once melted, add minced garlic and cook for 1-2 minutes until fragrant but not browned. Pour in chicken broth to deglaze the pan, scraping up any browned bits. Stir in heavy cream and remaining 2 tablespoons of butter.

Bring the sauce to a gentle simmer. Stir in grated Parmesan cheese until melted and smooth. Add the cooked chicken back to the skillet along with the drained pasta. Toss everything together, adding reserved pasta water as needed to reach your desired sauce consistency.

Remove from heat. Stir in chopped parsley and remaining salt and pepper. Taste and adjust seasoning if needed. Serve immediately garnished with additional parsley and Parmesan cheese.