Place the boneless skinless chicken breasts into your slow cooker. Pour in 2 cups of low-sodium chicken broth, followed by 1 cup of heavy cream. Add 2 tablespoons of salted butter, 4 minced garlic cloves, 1 teaspoon of kosher salt, and 1/2 teaspoon of black pepper. Set the slow cooker to low and let it cook for 4 to 5 hours until the chicken is tender and easily shredded.

Carefully remove the chicken breasts from the slow cooker using tongs and place them on a cutting board. Using two forks, shred the chicken into bite-sized pieces. Return the shredded chicken back into the slow cooker, stirring it into the creamy mixture to combine the flavors.

Add 12 ounces of rigatoni pasta to the slow cooker, ensuring it’s submerged in the creamy sauce. Stir gently to combine the pasta with the liquid, cover the slow cooker, and switch it to high. Cook for an additional 30 minutes, or until the pasta is tender.

Stir in 1 cup of freshly grated Parmesan cheese until melted and creamy. Give everything a good mix to ensure it's well-combined and the cheese has melted evenly throughout.

Scoop generous portions into bowls and garnish with freshly chopped flat-leaf parsley and additional Parmesan cheese, if desired. Serve hot with a side of garlic bread or a fresh salad.