01 - Generously season the chicken breasts on both sides with salt, black pepper, and dried Italian herbs.
02 - Place the chopped onion, minced garlic, and sun-dried tomatoes evenly in the base of the slow cooker.
03 - Arrange the seasoned chicken breasts on top of the vegetables in the slow cooker.
04 - Pour the chicken broth and heavy cream over the chicken. Place unsalted butter in small pieces on top.
05 - Cover and cook on low setting for 4 hours, or on high setting for 2 hours, until chicken is thoroughly cooked and tender.
06 - Transfer the cooked chicken to a platter. Stir grated parmesan cheese and fresh spinach into the hot sauce in the slow cooker. Allow spinach to wilt, about 5 minutes.
07 - Return chicken to the slow cooker, spoon sauce over the chicken, and continue to cook on low for another 5 to 10 minutes. Serve warm, topped with additional parmesan if desired.