Place peaches in a single layer on the bottom of roasting pan. Set aside.
Score skin and fat layers of ham in a diamond pattern with a paring knife. Place on top of peach slices.
Cover with aluminum foil. Insert an oven-safe probe thermometer into the center, but not touching bone.
Bake at 250 degrees until internal temperature reaches 130 degrees.
Meanwhile, combine remaining ingredients in a large saucepan. Bring to a boil over high heat until reduced by 1/3. Fish out ginger and bay and set aside.
Remove skin and fat layers off of ham. Pour peach mixture into pan and toss ham to coat. Remove aluminum foil and thermometer. Reinsert thermometer into a different area and bake at 350 degrees until internal temperature reaches 140 degrees. Remove and let rest 1/2 hour before carving.