Spoon the glaze over the top of the ham, fat side facing up in a plastic roasting bag. secure the bag, and roast the ham until it reaches at least 130 degrees. Remove the ham from the bag, pour the ham drippings into the roasting pan and remove the bag!
Place the roasting pan with pan drippings on a stovetop and set to medium heat. Add potato water to the roasting pan. Mix together cornstarch with a small amount of water to create a slurry and whisk it into the roasting pan