01 - Pat the chicken breasts dry and season both sides evenly with salt, pepper, and dried Italian herbs.
02 - Scatter the chopped onion, minced garlic, and chopped sun-dried tomatoes across the bottom of the slow cooker insert. Place the seasoned chicken breasts on top of the vegetable layer.
03 - Pour the chicken broth and heavy cream evenly over the chicken. Dot the surface with small pieces of the unsalted butter.
04 - Cover the slow cooker and cook on the LOW setting for 4 hours (or on HIGH for 2 hours), until the chicken is fork-tender and reaches an internal temperature of 165°F.
05 - Carefully remove the chicken breasts and set aside. Stir the grated Parmesan cheese and fresh baby spinach into the sauce inside the slow cooker. Allow the spinach to wilt, about 5 minutes.
06 - Return the chicken breasts to the slow cooker, spooning the creamy sauce over the top. Cover and let cook for an additional 5 to 10 minutes to allow the flavors to meld.
07 - Serve the chicken hot, spooned generously with the Tuscan cream sauce. Garnish with extra Parmesan if desired, alongside mashed potatoes, pasta, or crusty bread.