Place turkey between two pieces of parchment paper. Using a mallet or rolling pin, pound the turkey breast to a thickness of about 1/2 to 1 inch, then remove top piece of parchment.
Starting in the center of the turkey, cover with Proscuitto, leaving a border or edge of about 1 inch on all sides that is ham-free.
Sprinkle with sage and salt and pepper to taste.
Starting on the shortest side of the flattened turkey, roll it up jelly roll style into a tube or cigar-shaped log and tie it with string in about 3 or 4 places to hold the roll in place.
Pour wine and broth into slow cooker, then carefully lower turkey log on top.
Cover and cook on low heat setting for 5 to 6 hours.
Remove turkey from slow cooker and let sit for about 5 minutes before slicing.