In a large skillet, brown chicken in butter in batches. Transfer to a 5- or 6-qt. slow cooker. In a large bowl, combine the broth, heavy cream, onion, garlic, Italian seasoning and pepper; pour over chicken. Cover and cook on low for 4-5 hours or until chicken is tender.
Remove chicken to a cutting board. When cool enough to handle, shred with two forks. Keep warm.
Meanwhile, add pasta to slow cooker. Cook on low until pasta is tender, 20-25 minutes. Add chicken back to slow cooker, stir to combine. Serve with shredded Parmesan cheese.