90 minutes before baking ham start by soaking ham in hot tap water. Leave ham in its original packaging(If there is a hole or tear in the original wrapping, wrap it in several layers of plastic wrap before soaking it in hot water), cover with hot tap water; set aside for 45 minutes. Drain and cover again with hot tap water; set aside for another 45 minutes. You can bypass these steps, but the heating time will increase 18 to 20 minutes per pound for a cold ham.
Place oven rack in the lowest position and preheat oven to 275 degrees.
Open ham and place in oven bag. Gather top of bag tightly so bag fits securely around the ham, tie bag and trim surplus plastic. Set ham cut side down in large roasting pan and cut 4 slits in top of bag.
Bake ham until cetner registers 100 degrees, 1 to 1 1/2 hours (about 10 minutes per pound).
GLAZE: Combine all ingredients in saucepan. Cook over medium heat, stirring occasionally, until mixture is thick, syrupy about 5 to 10 minutes. There should be about 1 cup. Set aside.
Remove ham from oven and increase oven temp. to 350 degrees. Cut open oven bag and roll back sides to expose ham. Brush ham with 1/3 glaze and return to oven until glaze gets sticky, about 10 minutes.
Remove ham from oven, transfer to carving board, and brush entire ham with another third of glaze. Let ham rest, loosely tented with aluminum for 15 minutes.
While ham rests, heat remaining third of glaze with 4 to 6 tablespoons of ham juices until it forms thick but fluid sauce. Carve and serve ham with remaining sauce at table.