1 Place the ham in an oven preheated to 325°F for 20 to 25 minutes per pound or until internal temperature reaches 155°F on a meat thermometer. 2  Be sure the cooking bag is not touching the sides or top of the oven, otherwise the bag might melt. 3  Remove the ham from the oven and discard the bag and drippings.ncovered: 1  After trimming the skin and some of the fat, place the ham on a rack in a shallow baking pan with fat side up. 2  Half hams should be placed with cut side down. 3  Add 1/4 inch of water to the bottom of the roasting pan.