Let ham come up to room temperature: Unwrap the ham, and let sit at room temperature for at least 1 hour and up to 2 hours.
Bake the ham: Meanwhile, position a rack in the lower third of the oven, and preheat the oven to 300°F. Place the ham, flat-side down, in a roasting pan or other shallow baking pan. Pour water into the pan to a depth of ¼ inch. Cover tightly with foil. Roast 12 to 15 minutes per pound, or until an instant read thermometer inserted into the thickest part of the meat registers 130°F. Remove the ham from the oven and uncover. Increase the oven temperature to 425°F.
Prepare the glaze: While the ham bakes, stir together the brown sugar, honey, mustard, cinnamon, and allspice in a small bowl.
Glaze the ham: Spoon one-third of the glaze over the ham, and roast for 10 minutes. Repeat. Then, spoon the rest of the glaze over the ham and roast for 15 minutes or until the glaze sizzles and begins to form a crust.
Let rest before serving: Let the ham rest for 20 to 30 minutes before serving. Baste frequently with the pan juices, which will thicken as they cool. Serve warm, drizzling the slices with pan juices.
