In a large bowl, combine the chicken stock, lemon juice, lemon zest, garlic, sea salt, and black pepper. (The mixture may curdle slightly.)

Slowly add the melted butter to the lemon mixture and stir to combine.

In a slow cooker, place the chicken breasts.

Pour the lemon butter mixture over the chicken. Cover and cook on LOW for 6 hours or on HIGH for 3 hours, until the chicken is very tender.

Remove about 1 cup of the lemon butter mixture from the slow cooker and transfer to a small bowl. Add the xanthan gum to the 1 cup lemon butter and stir to combine. Return the mixture to the slow cooker.

Add the Parmesan cheese and heavy cream and stir well. Cover and cook on LOW for 1 hour or on HIGH for 30 minutes.

Top with the chopped parsley and serve.