01 - Place chicken breasts in the bottom of the slow cooker. Season evenly with salt, pepper, and dried Italian herbs.
02 - Scatter chopped onion and minced garlic over the seasoned chicken.
03 - Pour chicken broth and heavy cream into the slow cooker. Distribute cream cheese cubes and butter pieces across the top.
04 - Cover and cook on low setting for 4 hours until chicken is fully cooked through and tender.
05 - Remove cooked chicken breasts from the slow cooker. Using two forks, shred the meat into bite-sized pieces. Return shredded chicken to the pot.
06 - Stir uncooked fettuccine into the sauce, submerging pasta as completely as possible.
07 - Sprinkle freshly grated Parmesan cheese over the mixture and stir thoroughly to combine.
08 - Cover and cook on high for 25–35 minutes, stirring once or twice during cooking, until pasta reaches al dente texture and sauce is thickened.
09 - Serve immediately, garnished with freshly chopped parsley.